diabetes research and clinical practice 106 (2014) e14–e16

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Diabetes Research and Clinical Practice jou rnal hom ep ag e: w ww.e l s e v i er . c om/ loca te / d i ab r es

Response to Letter to the Editor

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Prevalence(%) of people with diabetes by sex and age, 2013

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Prevalence,%

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Female Male

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We thank the authors for raising an important issue in their letter concerning gender differences in prevalence of diabetes for 2013 [1]. The estimates produced are a product of a pooling and extrapolation of population-based studies [2]. For the latest estimates, there is little difference in the global estimates of diabetes between men and women in terms of cases (Male – 197.7 million, Female – 184.1 million), prevalence (Male – 8.7%, Female – 8.1%), and age-specific prevalence (Fig. 1). However, as the authors noted, differences in prevalence by gender emerge in some of the national estimates, with the largest differences seen in the North America and Caribbean Region (NAC) and Middle East and North Africa Region (MENA). We will briefly discuss the studies from which the estimates were derived where the largest gender disparities are seen. Estimates of prevalence in Belize were derived from a national health survey, which sampled the entire country, and obtained a high response rate for the self-reported portion (93%) and a moderate response for anthropometry (67%). The sample obtained even distribution by age and gender resulting in robust estimates for diabetes prevalence. In both selfreported diabetes and including results from fasting blood glucose measurement, the prevalence of diabetes was more than twice as high in women than in men [3]. This is suggestive of a true difference in diabetes prevalence in this population. Results from the other two major Caribbean populations are less clear. The STEPs report from St Kitts and Nevis [4] did not achieve the necessary sample size and thus was underpowered. Furthermore, 62.9% of the total sample was female, suggesting differential response rates between men and women. This can make direct male–female comparisons difficult, as the males and females in the study may represent different sub-sections of their respective total populations. Thus the 2:1 ratio of women to men in the self-reported prevalence may be the result of problems with the sampling as much as a true result. Similarly, the prevalence survey conducted in Port-au-Prince [5] reported a low response rate (69%) and 77% of participants were female. The resulting 2:1 ratio in prevalence (Men – 7.4%, 95% CI:

2.8–12.0%; Women – 11.1%, 95% CI: 7.5–14.7) could also be a result of sampling issues, which the authors of the study recognized in the limitations. The wide confidence intervals also indicate that prevalence differences between males and females were not significant. For countries in the MENA region, the results are less suggestive of a true difference for the region. Three large studies with robust samples for both men and women in Saudi Arabia by al-Daghri and colleagues [6], al-Nozha and colleagues [7] and conducted by the Ministry of Health [8] showed a significantly higher age-adjusted prevalence of diabetes in men than women, although the ratio is relatively small for all studies (1.21, 1.21 and 1.14, respectively). Al-Daghri et al. postulated that there maybe an unequal distribution of risk factors for men than for women in that country. By contrast, large well-sampled studies from the United Arab Emirates [9], and Oman [10] found no significant differences in the prevalence of diabetes between men and women. Regardless, studies from all over the world often report differences in prevalence by gender and there are several factors that may be driving these differences. Two major domains emerge: methodological and biological.

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Determinants of gender differences in the prevalence of diabetes

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Age (years)

Fig. 1 – Source: IDF Diabetes Atlas, 6th Edition, 2013, Brussels, Belgium. Printed with permission.

DOI of original article: http://dx.doi.org/10.1016/j.diabres.2014.07.012

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diabetes research and clinical practice 106 (2014) e14–e16

1.

Methodological determinants

The majority of estimates are based on data drawn from studies taking a sample of the total population for a particular sampling frame. With that approach come all of the limitations and uncertainty associated with a study using sampling. If the stratified sample drawn has adequate response rates and sample for each of the strata, the estimates remain reliable. However, this is not always the case and we have noted that many studies of diabetes prevalence sample fewer men than women. In some extreme cases, 4 times as many women as men participated in a study [11], but even in some of the largest studies, the sample size is almost always larger for women than for men. Where the sample size is low, selection bias may have a significant effect on the estimate. This bias is almost impossible to correct for once it has been introduced. Selection bias may also be introduced in the way a sample was obtained, the time of day for sampling, and at the point of data collection, all of which are very difficult to discern from a manuscript. Where studies only report known diabetes, differential access to care in the health system may affect disparities in prevalence between men and women [12]. These differences are very difficult to adjust for in the methodology as the evidence is lacking for percentage of undiagnosed diabetes, which is rarely reported by age and gender.

2.

Biological and demographic determinants

There are a number of contributors to prevalence beyond just the development of new cases (incidence) and one of the most important of these is mortality. Where there is a differential mortality for men and women, this will result in differences in prevalence for diabetes. A greater overall survival in women at older ages leads to a higher prevalence for women than for men. There is evidence of differences in the relative risk of death from diabetes for men and women, which have been incorporated into the mortality estimates presented in the Atlas [13] but are also confounded by the greater overall risk of death for men from all-causes. Some large, nationally representative studies have shown a higher prevalence in men than women [14–17] and some show the opposite relationship [6,18–20], with varying degrees of magnitude but it is not immediately clear what may be driving these differences or if they are a true reflection of an underlying biological differences by gender or if demographics are playing a role.

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Conclusion

We strongly support the authors in their call for more wellconducted population-based studies on the prevalence of diabetes. A careful adherence to sound sampling methodology and obtaining adequate sample size for strata by age and sex are essential to the strength of the estimates. Further high-quality research taking into account response rate and sampling will clarify whether gender differences are a

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result of biology, differential access to prevention or exposure to risk factors, or whether the differences that have been found in the past are a reflection of selection bias in data collection and underrepresentation of a gender.

references

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L. Guariguataa,* J.E. Shawb D.W. Whitingc U. Linnenkampa a International Diabetes Federation, Brussels, Belgium b Baker IDI Heart and Diabetes Institute, Melbourne, Australia c Directorate of Public Health, Medway Council, Chatham, United Kingdom *

Corresponding author E-mail address: [email protected] (L. Guariguata) Available online 15 August 2014 http://dx.doi.org/10.1016/j.diabres.2014.08.008 0168-8227/# 2014 Elsevier Ireland Ltd. All rights reserved.

Determinants of gender differences in the prevalence of diabetes.

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