Nutritional treatment for traumatic brain injury.

Journal of Neurotrauma Nutritional treatment for traumatic brain injury (doi: 10.1089/neu.2013.3234) This article has been peer-reviewed and accepted for publication, but has yet to undergo copyediting and proof correction. The final published version may differ from this proof.

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1 Title: Nutritional treatment for traumatic brain injury.

Angus G. Scrimgeour Ph.D. and Michelle L. Condlin M.A.,R.D. Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA.

Angus Scrimgeour*, Military Nutrition Division, USARIEM, Kansas Street, Natick, MA 01760; Tel: 508-233-5155; Fax: 508-233-4869; E-mail: [email protected]

Michelle Condlin, Military Nutrition Division, USARIEM, Kansas Street, Natick, MA 01760; Tel: 508-233-5685; Fax: 508-233-4869; E-mail: [email protected]

*corresponding author. Running title: Nutrition support for TBI. Table of Contents title: Nutritional treatment for traumatic brain injury.


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2 ABSTRACT – Traumatic brain injury (TBI) is a significant public health concern. On average, 1.7 million people sustain a TBI annually and about 5.3 million Americans are living with a TBIrelated disability. As the leading cause of death and disability in persons under 45 years old, there is a need for developing evidence-based interventions to reduce morbidity from this injury. So far, despite encouraging preclinical results, almost all neuroprotection trials have failed to show any significant efficacy in the treatment of clinical TBI. The cascade of molecular and cellular changes following TBI involves plasticity in many different neurochemical systems, which represent putative targets for neurotherapeutic interventions. Accordingly, a successful TBI treatment may have to simultaneously attenuate many injury factors. The purpose of this review is to highlight four promising nutritional intervention options that have been identified, omega-3, zinc, vitamin D and glutamine, and to provide an up-to-date summary regarding their apparent efficacy for affecting TBI.

KEYWORDS – traumatic brain injury, review, omega-3, zinc, vitamin D, glutamine.


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3 INTRODUCTION – Traumatic brain injury (TBI) is a contributing factor to a third of all injuryrelated deaths in the U.S. The estimated economic cost of TBI in 2010 (including direct and indirect medical costs), is estimated to be $76.5 billion 1. The incidence of mild TBI in combat casualties has prompted recognition for the establishment of measures to increase TBI recovery methods to hasten safe re-entry into the workforce, and treatments to minimize long-term and delayed TBI-related debilitation. So far, despite encouraging preclinical results, almost all pharmaceutical trials have failed to show any significant efficacy in the treatment of clinical TBI. This may be due, in part, to the fact that most of the therapies investigated have targeted an individual facet of the injury. It is now recognized that TBI is a very heterogeneous type of injury that varies widely in its etiology, clinical presentation, severity and pathophysiology. The pathophysiological sequelae of TBI are mediated by an interaction of acute and delayed molecular, cellular and physiological events that are both complex and multifaceted 2. Accordingly, a successful TBI treatment may have to simultaneously attenuate many injury factors.

We postulate that nutritional approaches are set to meet this need, playing an important role in future management options for mild-to-moderate TBI, and hence this contribution reviews recently published data describing nutrition-related recommendations for patients with mild or moderate TBI 3;4, suggesting that targeted nutrient therapy may promote functional recovery following TBI. Although the benefits of nutritional support in critical illness are widely accepted and supported by objective reviews of the evidence, the limited provision of nutritional support to neurotrauma patients was recently documented to be suboptimal 5;6. To convince more clinicians to provide enhanced nutritional support to neurotrauma patients, “better” evidence may


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4 be needed, as critically ill patients admitted with TBI are believed to be at the highest risk of delayed gastric emptying 7 and feed intolerance (prevalence of up to 80 %; 3;5). Although the current Brain Trauma Foundation Guidelines do not make a definitive statement on specific nutritional formulations to improve the outcome of mild-to-moderate TBI patients, they do recommend that patients with severe TBI receive their goal nutrition support by at least day 7 of injury 8. There are also data indicating that morbidity and mortality are decreased in patients receiving early feeding compared with those given standard nutritional treatment 9-11. However, the evidence is still not strong enough to establish a standard 3;12;13, and evidence is lacking for the post–acute rehabilitation period.

Intervention studies conducted using four different nutrients, namely omega-3, zinc, vitamin D and glutamine, will be reviewed. Understanding that nutrients will not be the sole treatment for TBI, and that it is a potentially powerful adjunct to promote neuro-repair, the four diet components reviewed were selected based on our review of the effectiveness of all the IOMrecommended diet components as monotherapies, targeted to a single factor/pathway 6. The 2011 IOM report also includes recommendations for using antioxidants, BCAA, choline, creatine, magnesium, and polyphenols. As most drugs aimed at select pathways of injury have achieved little, if any, success in larger clinical trials, treatments with broader, pleiotropic effects need to be explored. We concur with Loane 14, that mild TBI, with its intrinsic heterogeneity, may require multi-potential approaches to target multiple components of the secondary TBI injury cascade. Finally, we also considered uptake – as the four diet components reviewed can be readily taken up by the brain, and can be orally administered in addition to the parenteral route. Due to the complex and multi-factorial nature of TBI, we contend that a combination of


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5 putative beneficial dietary components would simultaneously act on multiple disease processes to effectively treat the neuroinflammation associated with mild-to-moderate TBI. Major deficiencies are highlighted, and possible dietary supplementation solutions are presented.


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6 OMEGA-3: n-3 polyunsaturated fatty acids (PUFAs) are important structural components of cell membranes, modulating membrane fluidity, cell wall thickness, cell signaling, and mitochondrial function 15;16. Long-chain n-3 PUFAs, including eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3), are highly enriched in neuronal synaptosomal plasma membranes and vesicles 15. DHA, the predominant PUFA in the central nervous system (CNS), is readily retained in neuronal plasma membranes. In turn, neuronal DHA influences the phospholipid content of the plasma membrane by increasing production of phosphatidylserine and phosphatidylethanolamine, and by promoting neurite outgrowth during development and adulthood 17;18. However, in the modern Western diet, the principal dietary PUFA is not DHA, but alpha-linolenic acid (ALA, 18:3 n-3), which is obtained through ingestion of certain nuts and vegetable oils. The efficiency of the conversion of ALA to EPA, however, is much lower than the absorption of EPA from food containing it. Because EPA is also a precursor to DHA, ensuring a sufficient level of EPA on a diet containing neither EPA nor DHA is harder both because of the extra metabolic work required to synthesize EPA and because of the use of EPA to metabolize into DHA 19. EPA and DHA give rise to resolvins, and DHA is also a precursor for protectins (e.g. NPD1), both of which are potently neurotherapeutic and neuroprotective 20. Therefore, increased ingestion of dietary sources rich in EPA and DHA, such as cold-water fish species and fish oil, may help improve a multitude of neuronal functions, including long-term potentiation and cognition 21;22.

It is estimated that human beings evolved consuming a diet containing approximately equal amounts of n-6 and n-3 PUFAs (n-6:n-3 ratio of 1-2:1) 23;24. In contrast, the present-day Western diet is relatively deficient in n-3 PUFAs and very high in n-6 PUFAs (n-6:n-3 ratio of 10-20:1).


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7 Factors contributing to this shift include the increase in red meat consumption, decrease in fish consumption, and the industrial production of animal feeds rich in n-6 PUFAs, resulting in red meat rich in n-6 and poor in n-3 PUFAs. The same pattern is true for farm-grown fish, chicken meat and eggs, which along with consumption of ALA-enriched vegetable oils, further contributes to the present-day imbalance of n-6:n-3 23;24. The current Western diet is high in vegetable-derived, cholesterol lowering fatty acids as a result of the indiscriminate recommendation in 1988 to substitute animal fats for vegetable fats, aimed at lowering serum cholesterol concentrations 25. The net effect of these changes has led to an increase in the consumption of vegetable oils relatively high in n-6 fatty acids [for example, corn, cotton, peanut, soybean, sunflower, and safflower oils], instead of vegetable oils high in n-3 fatty acids [including canola, flaxseed and linseed oils]. Hence, the increased n-6/n-3 ratio, and most importantly, the CDC now estimates that up to 80% of the United States population is omega-3 fatty acid deficient. This shift can cause serious long-term health effects as the PUFA composition of cells involved in inflammatory responses (e.g. macrophages, neutrophils, monocytes, lymphocytes) and microglia in the brain vary in response to the dietary source. Specifically, the DHA content and the resultant ratios of proinflammatory eicosanoids (e.g. prostaglandins, thromboxanes, and leukotrienes) and neuroprotective docosanoids (e.g. NPD1) are directly impacted by diet 26;27. The question is how increased DHA levels can benefit the TBI brain. It is well known that TBI causes degradation of membrane phospholipids 28, resulting in disturbances in cellular membrane functions, and contributing to secondary neuronal injury 29. Recently, Wu and colleagues provided evidence that DHA supplementation increases DHA content in the brains of TBI rats, which may help preserve membrane fluidity and integrity and enhance cognitive function 30. In animal models of TBI, decreased levels of β-amyloid precursor


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8 protein, a marker of axonal injury, were observed after 1 month of dietary supplementation with DHA 31;32, and decreased axonal injury counts and apoptotic markers as well as improved memory have also been documented in rats with TBI when given prophylactic DHA for 30 days 33

. Synaptic membrane phospholipids are preferentially enriched in n-3 fatty acids, especially

DHA. Thus, increased dietary DHA content may help prevent the loss of DHA from membrane lipids, and thus reduce the oxidative damage to the plasma membrane. Hence the findings from Wu and colleagues in rats 30, suggest that DHA-induced effects could influence the relative vulnerability or resilience of an adult to TBI (see Table 1), but translation studies are needed. This is a critical and timely concern as recent reports identified a very low n-3 PUFA status among active duty U.S. military and has linked this nutritional deficiency to reduced cognitive performance and heightened neuropsychiatric disorders and suicide risk 34-36. Similar epidemiological comparisons have linked relative consumption of n-6 and n-3 PUFAs to cardiovascular and autoimmune disease 37;38. Such diet-derived vulnerabilities, which we hypothesize will extend to TBI, should be readily and safely correctible, so the results of this research are highly translatable. n-3 PUFA dietary supplements can be directly incorporated into the regular Western diet as prophylactic agents, given following mild-to-moderate TBI, and included in enteral feeding formulations for severe TBI victims.

Multiple preclinical studies have suggested that DHA and/or EPA supplementation may have potential neuroprotective benefits through a multitude of diverse, but complementary mechanisms 31-33;39;40. Preclinical studies reveal DHA to be a pleiotropic molecule with neuroprotective effects which involve inhibition of proinflammatory transcription factors (NFκB), repression of pro-apoptotic proteins (Bax), activation of anti-apoptotic proteins (Bcl-2),


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9 activation of neurotrophins (BDNF), reduction in excitotoxicity, inhibition of inflammatory gene expression, suppression of oxidative reactions, modulation of calcium and potassium channels, and suppression of amyloidogenesis 15;41-43. However, key issues influencing efficacy such as optimal timing, dosing, and the interplay among underlying neurobiological mechanism(s) are undefined; thus, n-3 PUFA use in most medical facilities is often arbitrary. Studies utilizing rodent models of experimental injury have shown that pre-injury dietary supplementation with fish oil effectively reduces post-traumatic elevations in protein oxidation, resulting in stabilization of multiple molecular mediators of learning, memory, cellular energy homeostasis and mitochondrial calcium homeostasis, and improvements in cognitive performance 39;40. The benefits of pre-injury DHA supplementation have been independently confirmed 32, and DHA administered following TBI has been shown to significantly reduce the number of swollen, disconnected and injured axons 31;33. Of note, DHA has also provided neuroprotection in experimental models of both focal and diffuse TBI 31-33;39;40. Studies in other neurotrauma models have revealed a variety of potential mechanisms for the neuroprotective effects of DHA, including the restoration of brain “homeostasis” following TBI 17;18;39;40;44-47.

Despite abundant laboratory evidence supporting its neuroprotective effects in experimental models, the role of dietary DHA and/or EPA supplementation in human neurological diseases remains uncertain. To date, there have been no clinical trials investigating the effects of DHA and/or EPA dietary supplementation on the treatment or prevention of the deleterious effects of TBI. Several population-based, observational studies have suggested that increased dietary fish and/or n-3 PUFA consumption may reduce risk for ischemic stroke 48;49, and randomized control trials (RCTs) have also demonstrated significant reductions in ischemic stroke recurrence 50, and


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10 reduced incidence of both symptomatic vasospasm and mortality following subarachnoid hemorrhage 51. A few studies, on the other hand, have found no statistically significant affirmation of neurological impairment following ischemic stroke 52 or reductions in epileptic seizure frequency 53;54. Thus, the clinical evidence thus far appears equivocal. However, the overall difficulty in controlling for basal dietary intake of PUFAs between experimental groups, lack of good study design and the significant heterogeneity of the studied patient populations makes all of these studies difficult to interpret. Nonetheless, the multi-mechanistic neuroprotective properties and the positive preclinical findings associated with n-3 PUFAsupplementation warrant well designed clinical trials to determine whether supplementation may improve outcomes following mild-to-moderate TBI.

Recommendations for OMEGA-3: Being an essential part of the human diet, omega-3’s are highly safe and well tolerated 55;56. While omega-3’s are readily taken up by the brain, and they can be orally administered in addition to the parenteral route 57;58, documentation of the factors determining optimal use is crucial. For example, the Institute of Medicine (IOM) notes that when taken orally, the effects of n-3 fatty acids are not evident for days to weeks because of their slow incorporation into cellular membranes 6. Hence, initiation of oral administration following TBI therefore may not be of immediate benefit. The U.S. Food and Drug Administration has confirmed the overall safety of fish oil – both DHA and EPA at levels up to 3.0 g/day are generally recognized as safe 59, while the American Heart Association has furthermore established intakes of 1.0 g of EPA and DHA from fish or fish oils for patients with cardiovascular disease, and supplements of 2–4 g for subjects with high blood triglycerides 60. Most clinical studies of DHA have employed a dose of 2–6 g/day, and no consistent adverse


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11 events have been observed in humans consuming from less than 1.0, up to 7.5g/day of DHA 61. Potential harmful effects of n-3 PUFAs, however, have been described in the literature. Due to the established anti-thrombotic action of these compounds, for instance, they may increase the risk of hemorrhagic stroke, as suggested by a necropsy-based study of four cases in Greenland 62. Multiple clinical trials have shown that high-dose fish oil consumption is safe, even in patients receiving other agents that may increase the risk of bleeding, such as aspirin and warfarin 63-65. The overall clinical data suggests that DHA at doses up to 6 g/day does not have deleterious effects on platelet aggregation or other clotting parameters in normal individuals, and fish oil does not augment aspirin-induced inhibition of blood clotting 61. Platelet function is, on the other hand, inhibited by DHA consumption in type 2 diabetics, but it is suggested that this may actually be of benefit to these individuals, especially when coupled with the other activities of DHA 66. Nevertheless, it may be prudent to discontinue high-dose supplementation in the setting of a TBI patient presenting with poly-trauma (e.g. an acute bleeding illness or at high risk for hemorrhagic stroke) or, as is frequently recommended with aspirin, warfarin, and clopidogrel, prior to planned invasive procedures with the highest risk for bleeding complications 67-70. While clinical studies thus far have not yet identified an effective omega-3 treatment strategy against secondary injury after traumatic insult to the brain has occurred 71, a recent, three-patient case report involved the “Neuroceutical Augmentation for TBI (NATBI) protocol”, using 2g of omega-3/day to successfully treat three severe cases of TBI 72. Each 1-gram capsule (Loveza, GSK) contained 38% DHA, 47% EPA, and 17% other fish oils in the form of the ethyl ester.


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12 ZINC: Zinc (Zn) is a life-sustaining trace element with structural, catalytic, and regulatory roles in neurobiology, and is required for normal mammalian brain development and physiology. Deficiency or excess of Zn contributes to alterations in behavior, abnormal CNS development, and neurological disease 73. In this light, it is not surprising that dietary Zn reportedly also shows both neurotherapeutic and neuroprotective roles in treating the underlying immune-excitotoxicity that occurs with mild-to-moderate TBI (see Table 1).

TBI victims reportedly exhibit significantly depressed serum Zn levels as well as increased urinary Zn excretion 74. Moreover, urinary Zn excretion was proportional to the severity of the brain injury, and mean urinary Zn levels were 14 times greater than normal values in the most severely injured patients. It has also been observed that patients with severe head injuries develop hypoalbuminemia and inflammation 75;76. Because albumin is the major serum transport protein for Zn, hypoalbuminemia would potentially impair both Zn transport and availability. Induction of cytokines such as interleukin-1 during the acute phase response may further compromise Zn availability and reduce Zn stores due to downregulation of genes of the proinflammatry cytokines including IL-1, IL-6 and TNF-α, suggesting that a good intracellular Zn homeostasis may reduce neuroinflammation or, at least, may better keep under control the inflammatory status 77. Given the apparent role of TBI in compromising Zn status, Young and colleagues 78 tested the effectiveness of using intravenous Zn supplementation in 68 patients following TBI to offset Zn losses and maintain protein balance in an attempt to improve neurological outcomes. Zn supplementation resulted in increased levels of serum pre-albumin and retinol-binding protein, suggesting improved visceral protein synthesis in TBI patients. Two weeks after injury, patients in the Zn-supplemented group had better Glasgow Coma Scale


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13 (GCS) scores than control patients given adequate Zn, and improvements were maintained at 21 and 28 days. Interestingly, the differences between the groups were seen despite the fact that neither serum Zn concentrations nor Zn levels in cerebral spinal fluid were changed by Zn supplementation, suggesting that the Zn is taken up into tissues after administration, and illustrating the fact that serum Zn levels are not a good indicator of Zn status 79.

As many as 40 % of patients hospitalized with TBI develop major depression, making it the most common long-term complication of TBI 80, and depression is associated with a lower concentration of Zn in peripheral blood 81. Involvement of Zn in antidepressant therapy, which was indicated by animal experiments, has some clinical correlates. Multiple groups report that human depression might be accompanied with lower serum Zn concentrations 82-84. These findings were confirmed by Maes 85, who found that the subjects suffering from major depression showed significantly lower serum Zn levels than non-depressed controls. Interestingly, they also observed that the patients with minor depression showed intermediate Zn levels. Moreover, the unipolar depression was not only associated with lower blood Zn levels, but the severity of the illness [expressed according to Hamilton Depression Rating Scale (HDRS)] was negatively correlated with serum level of this ion 85;86. The findings that the lowered serum Zn concentrations may be normalized after successful antidepressant therapy 87;88 further support the notion that serum Zn concentrations are a sensitive and specific marker of depression. A recent systematic review of four RCTs on the efficacy of Zn supplementation for reducing, or preventing depressive symptoms suggests potential benefits of Zn supplementation as a stand-alone intervention or as an adjunct to conventional antidepressant drug therapy for depression 89. Although there are no data on the use of supplemental Zn to reduce or prevent


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14 depressive symptoms in patients with TBI-associated depression, the use of Zn to improve mood may be effective among this patient population.

Experimental evidence indicating a possible role for the use of Zn as a treatment in TBI was obtained using a rodent model to test the hypothesis that Zn supplementation before injury could increase resilience and improve brain-injury outcomes 90. A controlled cortical injury (CCI) model of TBI in adult rats induced anhedonia, a depression-like symptom in the rat, and although this symptom was observed in injured animals fed a diet with adequate Zn (30 ppm, or 15 mg/d), four weeks of Zn supplementation (180 ppm, or 90 mg/d) before the injury prevented the appearance of anhedonia following TBI. CCI also produced anxiety-like behaviors; however, animals fed the Zn-supplemented diet prior to injury appeared to have greater resilience to injury-induced anxiety. This study also examined whether Zn supplementation could prevent TBI-associated losses in spatial learning and memory, and while CCI resulted in significant performance deficits on the Morris Water Maze test, rats that were fed the Zn-supplemented diet prior to TBI showed no differences from sham-operated control rats suggesting that Zn supplementation may improve cognitive resilience to TBI 90.

A concern for nutritionists arises from reports that high concentrations of free Zn are neurotoxic. Specifically, the accumulation of free Zn following TBI in animal models appears linked to neuronal injury 91;92. In brief, the free Zn, sequestered in synaptic vesicles, is released from neurons into the synaptic cleft where it results in postsynaptic neuronal death 93. Although the release of synaptic Zn after injury is well accepted in the field, there have been indicators that other pools of free Zn may contribute to neuronal damage after injury. For example, using an in-


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15 vitro model of ischemic brain injury in which cells were exposed to 3h of oxygen-glucose deprivation (OGD) followed by incubation under normal conditions, free Zn levels were quantified with radiometric mitochondrial and cytoplasmic Zn sensors. Mitochondrial free Zn levels 1h after OGD increased to 10pmol/l from 0.2pmol/l at control levels, whereas at the same time cytosolic free Zn concentrations were decreased significantly. Mitochondrial free Zn eventually tapered off to normal physiological levels by 2h after OGD, whereas cytosolic free Zn gradually increased by about 10-fold, 24h after OGD 94. This work suggests that changes in the subcellular localization of free Zn following neuronal injury are complex and are likely to have a significant impact on neuronal survival. The data provide further evidence that disruption of Zn homeostasis during a brain injury can be detrimental to the survival and viability of neurons. It is worth noting that investigations are ongoing to develop clinically relevant treatments to prevent Zn-mediated neuronal death. A 3h pretreatment of mouse hippocampal primary neurons with urokinase plasminogen activator (uPA), a serine protease that converts plasminogen to active plasmin, inhibited Zn-induced cell death. Thus, future work should be conducted to determine the extent to which uPA can be utilized as a potential treatment and neuroprotective agent in Zn-induced cellular and neuronal damage 95. In addition to affecting the site of injury, TBI produced either by fluid percussion injury 91 or mechanical cortical trauma 96 resulted in neuronal death in the dentate gyrus, hilus, and CA1 regions of the hippocampus. The neuronal injury appears to be associated with presynaptic Zn release 97, and the cell death was largely prevented by treatment with the Zn chelator calcium disodium EDTA 91;98, hence the suggestion that Zn in high concentrations following TBI is neurotoxic. These dual neurotoxic and neuroprotective effects of Zn are widely known 99, but the precise mechanisms responsible for its neurotoxic and neuroprotective effects remain unclear.


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TBI induces a variety of damaging oxidative processes, and a number of studies show a role for Zn deficiency in the induction of reactive oxygen species (ROS). An understanding of the possible role of free Zn in neuronal death raises the question of whether clinicians should be treating brain-injured patients with supplemental Zn, particularly in acute periods after severe injury when the blood-brain barrier that regulates brain Zn uptake has been disrupted. Using an animal model of TBI, Yeiser 100 reported that 4 weeks of dietary Zn supplementation (180 ppm, or 90 mg/d) following TBI did not significantly increase cell death (as measured by TUNEL labeling) in any cell type examined, including microglia, macrophages, neurons, or oligodendrocytes at the site of injury or any other region of the CNS. These data suggest that concern about the potential neurotoxicity of enteral Zn supplementation in TBI patients is unwarranted. Reports that intraperitoneal injections of Zn significantly increased the infarct size and impaired motor behavior after focal ischemia in rats suggest, however, that caution is warranted when using Zn parenterally in moderate-to-severely injured patients 99;101.

Recommendations for Zn – Available clinical evidence suggests that in the acute care situation following TBI, Zn deficiency should be prevented to maintain visceral protein stores and to optimize the potential for neurological recovery. In patients with a moderate-to-severe brain injury, there are acute increases in urinary Zn excretion and significant decreases in serum Zn levels that have been shown to be proportional to the severity of injury 74. The only dose of supplemental Zn that has been tested in a clinical setting is 12 mg Zn-sulphate/day administered intravenously for the first 15 days after injury. After day 15, an oral dose of 22 mg/day was provided 78. Zn supplementation was associated with increased visceral proteins such as


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17 prealbumin and retinal-binding protein, and improvements in GCS scores were seen 2 weeks after the start of treatment 78. However, there have been no clinical trials to assess the efficacy of Zn as a treatment for mild TBI. With the Tolerable Upper Intake Level (UL) set at 40 mg/day 102

, these doses are not likely to have adverse effects. However, the impact of parenteral

administration of Zn has not been independently investigated, nor has it been compared to enteral feeding in a TBI model. The data does suggest that recommendations to supplement Zn for the treatment of mild-to-moderate TBI should include cautionary advice not to chronically exceed the UL for Zn intake. Considering the paucity of clinical trials, the data strongly suggest that Zn status should be monitored and maintained after a brain injury, not only because of the reported neurocognitive outcomes, but also because both Zn deficiency and TBI have been associated with oxidative stress 103;104.


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18 VITAMIN D: A fat-soluble vitamin that is essential for maintaining normal calcium metabolism, vitamin D is found in some foods including fish and egg yolks. Fortified foods such as milk and cereals provide most of the vitamin D in American diets. Vitamin D can also be manufactured in skin upon exposure to ultraviolet B rays from sunlight. Vitamin D is required to promote normal brain development, maintain pregnancy, and for skeletal development. However, the vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation. The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol 105;106.

Vitamin D deficiency is defined as serum 1,25(OH)2D of less than 30 nmol/L 106. A recent global review of vitamin D status has shown that its intake is often too low to sustain healthy circulating 1,25-dihydroxyvitamin D 105. Approximately one billion people worldwide are estimated to be vitamin D deficient with people living in Europe, the Middle East, China and Japan at particular risk 107;108, but vitamin D deficiency has become epidemic for all age groups in the United States and Europe 109;110. Vitamin D deficiency has been associated with inflammatory, autoimmune, cardiovascular, neuromuscular, and neurodegenerative diseases, as well as cancer 109, and population based studies suggest that vitamin D deficiency is associated with an increased prevalence of Parkinson's disease 111, dementia, Alzheimer's disease, and increased stroke risk in the elderly 112-114. Deficiency is more common in women than men (9.2 % vs. 6.6 %) and pregnancy is known to represent a particularly high-risk situation 115.


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19 Vitamin D deficiency may increase inflammatory damage and behavioral impairment following experimental injury and attenuate the protective effects of post-traumatic progesterone treatment 116

. There have been no clinical trials to assess the efficacy of vitamin D as a treatment for mild

TBI, but the studies by Buell 112 and Witham 117 using stroke victims are informative: Vitamin D insufficiency (serum levels between 10-20 ng/ml) was associated with twice the risk of stroke. These authors conclude that vitamin D insufficiency and deficiency is associated with all-cause dementia, Alzheimer disease, stroke (with and without dementia symptoms), and MRI indicators of cerebrovascular disease. These findings suggest potential neuroprotective and/or vasculoprotective roles for vitamin D that might have relevance to mild TBI (see Table 1). More recent research has suggested that vitamin D supplementation and the prevention of vitamin D deficiency may serve valuable roles in the treatment of TBI as a neuroprotective adjuvant for post-TBI progesterone therapy 109;116;118. Progesterone is one of the few agents to demonstrate significant reductions in mortality following TBI in human patients 119;120, and in vitro and in vivo studies have suggested that vitamin D supplementation with progesterone administration may significantly enhance neuroprotection 118;121. Both agents have high safety profiles, act on many different injury and pathological mechanisms, and are clinically relevant, easy to administer, and inexpensive. While there are two Phase III clinical trials underway evaluating the efficacy of intravenous progesterone for moderate-to-severe TBI 119;122, there is currently only one pilot study evaluating progesterone for the treatment of concussion/mild TBI (see www.clinicaltrials.gov). Our perspective is that the combination of progesterone and vitamin D should be considered in pre-clinical and clinical studies as a novel and compelling approach to TBI treatment.


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20 Numerous drugs with vitamin D activity are available for clinical use and it may not be easy for the non-specialist to select the most suitable for the individual patient. Available drugs with vitamin D-like activity are not all the same either in terms of pharmacological actions, and/or side-effects. They have specific characteristics that may be useful to know in order to operate the best choice in the individual TBI-patient. Natural vitamin D products are those identical to natural metabolites, while the most frequently used vitamin D supplements are synthetic molecules (i.e. bioengineered molecules not found in nature), which are generally referred to as "analogs". Either cholecalciferol, ergocalciferol or calcifediol can be employed in subjects with normal renal function to correct vitamin D-deficiency and improve, respectively, age- or growthrelated bone disease and secondary hyperparathyroidism. Calcifediol can be considered more rapid and effective. In all cases, especially with increasing doses, the risk of hypercalcemia must be taken into account. Calcitriol, which can be regarded as the active hormonal form of vitamin D, has the most potent hypercalcemic effect in both normal and renal failure patients. Calcitriol is best used in cognitive dysfunction, including dementia resulting from TBI 123. Importantly, reno-protective and cardio-protective effects of these analogs have been recently evaluated by means of RCTs in renal patients with partially positive renal effects and negative cardiac results – but no similar studies have been conducted in the TBI population.

Recommendations for vitamin D – Schnieders 124 recently reported that 65% of patients with varying degrees of TBI were vitamin D deficient i.e. having serum 25-OHD level < 30 nmol/L (using the Endocrine Society guidelines). Thus a vitamin D deficiency, combined with an omega-3 deficiency, may work synergistically to worsen outcome in patients with TBI. As both are very prevalent in the U.S. population, and even more pronounced in critically ill patients with


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21 TBI, at-risk patients should be routinely supplemented with vitamin D and omega-3, in our opinion.

The Food and Nutrition Board recommends that generally healthy adults take 600 IU (15 µg) of vitamin D daily 106, and conservatively set a tolerable upper intake level (UL) of 4,000 IU/day (100 µg) for all adults. While rapid correction of serum 25-OHD levels can be easily achieved with oral administration of high-dose cholecalciferol, most multivitamins contain 400 IU of vitamin D, and single ingredient vitamin D supplements are available for additional supplementation. The Vitamin D Council suggests that a serum level of ≥ 50 nmol/L is the ideal, and to achieve this, it is recommended that adults should take ≥800–1000 IU of vitamin D/day from dietary and supplemental sources 125-127, when sunlight is unable to provide it. Specific amounts of vitamin D are detailed in a recent clinical trial 128 that reported on using the combination of vitamin D (8.0 µg/L) and/or progesterone (6.3 µg/L) for treating patients with severe TBI (GCS

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