Unhealthy behaviours like being overweight, smoking and heavy drinking explain almost half of the social inequalities in type 2 diabetes, finds a study published on bmj.com today.

The authors say further efforts to tackle these risk factors, particularly excess weight, among disadvantaged groups are urgently needed.

The burden of type 2 diabetes disproportionally affects the lower socioeconomic groups in society. Lifestyle related risk factors are thought to play a key role, but previous studies have tended to underestimate their effect.

So an international team of researchers set out to measure the contribution of several major risk factors for type 2 diabetes to socioeconomic differences across society.

They assessed health behaviours (smoking, alcohol consumption, diet and physical activity), body mass index, and biological risk markers (blood pressure and lipid levels) in 7,237 middle-aged adults without diabetes, measuring these risk factors repeatedly over an average of 14 years.

All the study participants were taking part in the Whitehall II study, which is evaluating the impact of social and economic factors on the long term health of around 10,000 British civil servants, aged between 35 and 55 in 1985.

Socioeconomic status was assessed through occupational position and reflected education, salary, social status, and level of responsibility at work.

Over the average follow-up of 14 years, 818 cases of diabetes were identified. Participants in the lowest occupational category had a 1.86-fold greater risk of developing diabetes relative to those in the highest occupational category.

Health behaviours and body mass index explained up to 45% of this socioeconomic differential in both men and women when changes over time and long term exposure were accounted for. With additional adjustments for biological risk markers, a total of 53% of the socioeconomic differential was explained.

Body mass index was the most important single contributing factor, explaining about 20% of socioeconomic differences.

This finding is not surprising, say the authors, as weight gain is strongly socially patterned. However, the effects of diet and physical activity were smaller than expected, given that these behaviours are also strongly socially patterned, they add. The contribution of smoking and alcohol consumption was also modest.

They conclude: "Given the increasing burden of type 2 diabetes and the observed increase in social inequalities in prevalence of type 2 diabetes, further efforts to tackle these factors are urgently needed."