Wednesday October 5 2011
Men developed diabetes at lower BMIs than women
Researchers may have discovered why men may be more likely to develop type 2 diabetes than women, BBC News has reported. The broadcaster said that a new study has found men are biologically more susceptible and need to gain far less weight than women to develop the condition.
In the study, Scottish researchers examined the records of 95,057 men and women with type 2 diabetes (a condition caused by too much glucose, a type of sugar, in the blood), looking at their ages and body mass index (BMI) scores at the time of diagnosis. A clear trend was found in their results, with men developing type 2 diabetes at a lower BMI than women of a similar age.
The researchers have speculated on why this may be the case, and have offered theories that men may be less sensitive to insulin than women or that males tend to store fat around their organs rather than under the skin as women do. However, the proposed reasons are only theories and cannot be confirmed by this study, which examined a limited range of factors at a single point in time.
Overall, the observation that men seem to develop type 2 diabetes at a lower BMI than women of the same age is worthy of further exploration. As Dr Victoria King, Head of Research at Diabetes UK, told the BBC: "It is worrying that men develop type 2 diabetes at a higher rate than their female counterparts. Research like this will help us understand reasons why and provide greater insight into what we can do to improve prevention of type 2 diabetes."
Where did the story come from?
The study was carried out by researchers from several Scottish research institutes, including the Scottish Diabetes Research Network Epidemiology Group at the University of Glasgow. The research received funding from the Wellcome Trust.
The study was published in the peer-reviewed medical journal Diabetologia.
BBC News provided balanced coverage of this research.
What kind of research was this?
This was a cross-sectional study that looked at the associations between age, gender and BMI in men and women at the time of diagnosis of type 2 diabetes. The researchers wanted to test the hypothesis that men diagnosed with type 2 diabetes tend to have a lower average BMI than women diagnosed at a similar age, in other words, it that it takes less excess weight to trigger the condition in men than in women. The researchers said that this hypothesis was based on the fact that several recent studies have observed that European middle-aged men are at higher risk of diabetes than European middle-aged women. To test their theory they examined data on a large group of men and women from a population-based diabetes register in Scotland.
While this sort of study can observe trends in age and BMI at time of diagnosis and compare differences between men and women, it cannot tell us a great deal more than this. For example, it is not possible to determine the biological reasons why the men and women developed diabetes at the time they did, and the researchers' interpretations of their data are only theories at this stage. These theories provide an interesting discussion of the results and highlight areas for further study, but cannot be proven by this particular set of results.
What did the research involve?
The researchers looked at a 2008 snapshot of data held in the Scottish Care Information Diabetes Collaboration (SCI-DC) dataset, a population-based register holding information on people diagnosed with diabetes in Scotland. They were specifically interested in individuals with diabetes who had had their BMI measured within one year of diagnosis. Information on smoking status and blood glucose levels was also collected.
The researchers excluded data on individuals with a BMI of less than 25 and those diagnosed with diabetes before the age of 30 in order to try and limit inclusion of people with type 1 diabetes. They also excluded any remaining individuals who were missing data on key measures such as BMI, leaving them with a sample of 51,920 men and 43,137 women – representative of only 35.1% of the entire eligible dataset.
The researchers then used graphical models to plot BMI at the time of diagnosis against age at the time of diagnosis. Plotting separate graphs for men and women allowed them to compare whether associations between age and BMI at the time of diagnosis were different in men and women.
What were the basic results?
In the included sample of 95,057 individuals, men were on average significantly younger than women (average age 59.2 years versus 61.6 in women). The mean BMI recorded within a year of diagnosis of type 2 diabetes was 31.83kg/m2 in men and 33.69kg/m2 in women (a BMI of 25-29.9 indicates a person is overweight, and a BMI of 30 or above indicates obesity).
When the researchers plotted a graph of the relationship between average BMI and age at time of diagnosis, they observed clear trends: people with a higher BMI tended to develop type 2 diabetes at a younger age, and the BMI of women at the time of their diagnoses was consistently greater than that of men. This indicates that at a comparable age, men are developing diabetes at a lower BMI than women.
The researchers also adjusted their analysis to account for other factors that could have influenced the relationship. When they made adjustments to account for participants’ smoking they found it had no effect on their results. Men and women also had comparable blood glucose levels at the time of diagnosis, suggesting that these findings were not a consequence of men being diagnosed at an earlier stage of their condition.
The BMI gap between men and women was most significant at younger ages. According to the researchers’ graph, men who developed diabetes at age 40 had a BMI of around 34-35 versus 38-39 in women who developed diabetes at age 40. The gap gradually diminished as people got older, until eventually men and women who developed diabetes around the age of 80 of older had comparable BMI scores.
How did the researchers interpret the results?
From their analysis of a Scottish population of people with type 2 diabetes the researchers conclude that men are diagnosed with the condition at lower BMI than women of the same age. They suggest this observation could explain why type 2 diabetes is more common among middle-aged men in European populations.
This study is of scientific and medical interest and uses a large and reliable dataset to examine the associations between gender, age and BMI at the time of development of type 2 diabetes. The trend in the results is quite clear and supports previous studies which have observed that, despite higher prevalence of obesity in women, the prevalence of diabetes in middle-aged men exceeds that of women in some populations.
The study prompts further speculation about why this may be the case. For example, the researchers consider that for any given BMI, men may be less sensitive to insulin than women are. They also consider that it may be something to do with fat distribution, as men tend to distribute fat more readily around the liver and other body organs, while women tend to deposit fat under the skin (for example, around the hips and middle).
With regard to this latter theory, the researchers note a limitation of their study in that they did not have information on waist circumference. They say a previous study has suggested that women develop diabetes at a higher waist circumference than men.
However, the theories put forward cannot be proven by this study, which provides a snapshot of certain factors at the point of diagnosis but not an analysis of key factors that may have caused the condition to occur. In short, it is not possible to determine the reasons why these individuals developed diabetes when they did: to do so, other aspects of the individuals’ medical, lifestyle and family history would need to have been examined. The study paper also does not mention any analyses of dietary habits or alcohol consumption, which may be a key difference between males and females and also influence the way that individuals gain weight.
Also, it is not known whether the same findings would be observed in other populations. In particular, as the researchers note, it is not known whether the same pattern would be observed in people of other ethnic groups, as the Scottish sample included predominantly people of white European ancestry.
It is also worth noting again that, despite the large size of this Scottish sample it is still representative of only 35% of the total eligible dataset (the remainder being excluded as they were missing relevant data), and examining the whole sample could have given different findings.
Overall, the observation that men seem to be diagnosed with type 2 diabetes at a lower BMI than women of the same age is important, and warrants further study to establish why this may be the case.