A major new review study has shown that women with diabetes are 44% more likely to develop coronary heart disease (CHD) than men with diabetes.

This finding was independent of differences between the sexes in the levels of other major factors that put people at risk of developing heart disease.

The data used in the study by scientists in the UK, Australia and the Netherlands goes back nearly 50 years and takes in around 850,000 people.

The review found that women with diabetes were almost three times more likely to develop CHD compared to women without diabetes, while men with diabetes were only twice as likely to develop CHD than men without diabetes.

Combining the two sets of data demonstrated that women with diabetes were 44% more likely to develop heard disease than men with diabetes even after consideration was made for sex differences in other risk factors.

A number of possible reasons for the difference between the sexes are discussed by the researchers.

Women have, particularly in the past, been under-treated for risk factors for heart disease.

However, the authors point out that even in more recent years, when diabetes is treated similarly in women as in men, women have been less likely to reach treatment targets.

It is speculated that that women may have to metabolically deteriorate further than men to become diabetic, so they are at a worse starting point even before treatment begins.

Another reason for the difference may be that women who currently have diabetes, just before they develop diabetes ('pre-diabetes'), are believed to have a higher level of risk factors for future heart disease such as overweight/obesity.

The research, by scientists at the University of Queensland; University of Cambridge; University Medical Center Utrecht; and George Institute for Global Health, Sydney, Australia, is published in Diabetologia, the journal of the European Association for the Study of Diabetes.

A systematic review and meta-analysis of some 850,000 people published in Diabetologia (the journal of the European Association for the Study of Diabetes) shows that women with diabetes are 44% more likely to develop coronary heart disease (CHD) than men with diabetes independent of sex differences in the levels of other major cardiovascular risk factors. The research is by Professor Rachel Huxley, School of Population Health, University of Queensland, Australia; Dr Sanne Peters, University of Cambridge, UK, and University Medical Center Utrecht, the Netherlands, and Professor Mark Woodward, George Institute for Global Health, Sydney, Australia.

The data used in the study stretches back almost 50 years, from 1966 to 2011, and includes 64 studies, 858,507 people and 28,203 incident CHD events, Women with diabetes were almost 3 times more likely to develop CHD (actual relative risk 2.82) compared with women without diabetes, while men with diabetes were only twice as likely (actual relative risk 2.16) to develop CHD than men without diabetes. Combining the two sets of data showed that women with diabetes were 44% more likely to develop CHD than men with diabetes even after consideration was made for sex differences in other CHD factors.

The authors say that this study, the largest ever of its kind backs up findings from a smaller analysis including fewer studies that showed a 46% increased risk of dying from CHD in women with diabetes compared with men with diabetes. In this new analysis by Huxley and colleagues, the sex difference in diabetes-related risk for incident CHD was consistent across subgroups defined by age and region and remained unchanged after excluding non-fatal CHD events. They note that in another previous study they authored, diabetes in women increased the risk of stroke by 25% compared with diabetes in men. They say: "Taken together, these data provide convincing evidence that diabetes poses a greater relative risk for cardiovascular diseases in women than in men."

Several possible reasons for the difference are discussed by the authors. Women have, particularly in the past, been undertreated for risk factors for cardiovascular disease (evident in studies from 1985 and before). However, even in more contemporary populations, when diabetes is treated similar to men, women have generally been less likely to achieve treatment targets. The authors (along with others before them) speculate that women may have to metabolically deteriorate further than men to become diabetic, so they are at a worse starting point even before treatment begins. Furthermore, in the prediabetic state where glucose tolerance may already be impaired but does not meet all diagnostic criteria of diabetes, risk factor levels are more elevated in women than in men. For example, in the UK General Practice Research Database, the BMI of individuals at the time of diabetes diagnosis was, on average, almost two whole units higher (1.8 kg/m2) in women than in men.

The authors say: "It is conceivable, therefore, that the diabetes-related excess risk of CHD in women may be due to a combination of both a greater deterioration in cardiovascular risk factor levels and a chronically elevated cardiovascular risk profile in the prediabetic state, driven by greater levels of adiposity in women compared with men."