Obesity and lack of physical exercise as risk factors for type 2 diabetes receive a large amount of attention, but a recent American epidemiological study has shown another interesting risk factor. The Atherosclerosis Risk in Communities study has found that high parity is associated with insulin resistance and the onset of type 2 diabetes.

As part of a larger, population-based, prospective cohort study, 7,024 white and African-American women aged 45 to 64 years were investigated for diabetes at four sessions over a follow-up of nine years. Participants with diabetes at baseline were excluded. Parity was defined as the number of live births. Women were classified into groups of nulliparity (no live births), one or two births, three or four births and five or more births (grandmultiparity). A separate category, nulligravida, was included for patients who had never been pregnant. Results were adjusted for sociodemographic, clinical and lifestyle factors, including smoking, BMI and physical exercise, and also inflammatory markers.

The study found that the incidence of diabetes increased with parity, from 11.0 per 1,000 person-years in women with one to two live births to 23.3 per 1,000 person-years in women with grandmultiparity. After adjustment for covariates, grandmultiparity was associated with a 27 per cent increase in the risk of diabetes compared with having one or two live births.

This finding should be considered in conjunction with the recent concerns over the risks of pregnancy itself, which are substantially increased for the large numbers of women who are clinically obese when they become pregnant. These women are at an even greater risk of developing diabetes.

Nicholson, WK, Asao K, Brancati F, et al. Parity and risk of type 2 diabetes. Diabetes Care 2006;29:2349-2354