One of the largest studies to investigate the relationship between blood pressure and type 2 diabetes has found that women who have high blood pressure levels are three times more likely to develop diabetes than women with low blood pressure levels.
This effect was independent of body mass index and other conditions that are known to predispose people to cardiovascular disease and diabetes.
Writing in the European Heart Journal, the authors say that clinicians should be aware of the relationships between blood pressure and type 2 diabetes to optimise the management of patients at increased risk for cardiovascular disease.
The researchers from the Brigham and Women's Hospital, Harvard Medical School and the Harvard School of Public Health, USA, followed over 38,000 female health professionals for ten years. At the start of the study in 1993, all the women were free of diabetes and cardiovascular disease. Follow-up continued to the end of March 2004, at which point data were nearly 100% complete (97.2% for morbidity and 99.4% for mortality).
The lead author, Dr David Conen, a cardiologist and research fellow, explained: “Despite several studies finding a close relationship between hypertension and type 2 diabetes, little information exists on the relationship between blood pressure levels and the subsequent development of type 2 diabetes. Data for women are particularly limited. Finding an independent association between blood pressure and new-onset diabetes is important, because it suggests that women with increasing blood pressure levels should have their blood glucose levels monitored. Individuals at high risk for cardiovascular disease may benefit from early intervention.”
The researchers divided the women into four groups: those with optimal blood pressure (BP), below 120 mmHg systolic, 75 mmHg diastolic; those with normal BP (120-129 mmHg systolic, 75-84 mmHg diastolic); those with high normal BP (130-139 mmHg systolic, 85-89 diastolic); and those with established hypertension (at least 140 mmHg systolic, 90 mmHg diastolic, and/or self-reported history of hypertension or treatment for the condition).
After 10 years of follow-up 1.4, 2.9, 5.7 and 9.4% of women in the four categories respectively had developed type 2 diabetes. After adjusting for various factors such as age, ethnicity, smoking, alcohol intake, body mass index (BMI), exercise, family history of diabetes etc, the researchers found that women with hypertension had a three-fold risk of developing diabetes compared with women with optimal BP.
Dr Conen said: “We found that obesity was also a strong and independent risk factor for the development of type 2 diabetes. However, statistical analyses showed that the relationship between blood pressure and the onset of type 2 diabetes was similar among women who were normal weight, overweight or obese. There was a three-fold increase in risk from the lowest to the highest BP category within all three weight categories. This analysis showed that the association between blood pressure and diabetes was not explained by weight alone.”
Women who had an increase in BP during the study also had an increased risk of developing diabetes. Those whose BP rose but who remained within the range of normal BP had an increased risk of 26% compared to women who had stable or decreasing BP. Women who progressed to hypertension had a 64% increased risk.