Almost 30,000 women provided data about their dietary intakes and then followed for about 10 years, with the risk of hypertension inversely linked to dietary calcium and dietary vitamin D intakes, researchers report in the journal Hypertension.
"Our study findings offer additional support to [2005 Dietary Guideline from the US Department of Agriculture recommend that the majority of Americans increase their intake of milk and milk products to three servings per day] from the perspective of hypertension prevention and emphasize on the importance of low-fat dairy products," wrote lead author Lu Wang.
"Because hypertension remains a highly prevalent disease in the US, even a modest reduction in hypertension risk on individual level will substantially."
High blood pressure (hypertension),defined as having a systolic and diastolic blood pressure (BP) greater than 140 and 90 mmHg, is a major risk factor for cardiovascular disease (CVD) - a disease that causes almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169bn ($202bn) per year.
The new research recruited 28,886 women with an average age of 54 and assessed their dietary intakes using a semi-quantitative food frequency questionnaire (FFQ). Over the course of ten years of follow-up 8,710 cases of hypertension were recorded.
Wang and co-workers report that women with the highest average intakes of low-fat dairy (between 2.0 and 9.6 servings per day) were 11 per cent less likely to develop hypertension, compared to women with the lowest average intake (less than 0.27 servings per day).
Moreover, reductions in the risk of hypertension were reported for both dietary calcium (13 per cent decrease) and dietary vitamin D (five per cent decrease). However, the benefits were not found when the researchers considered supplemental calcium and vitamin D.
On the other hand, high-fat dairy products were not associated with any changes in the risk of hypertension.
"It remains unclear why benefits are observed for low-fat dairy products but not for high-fat dairy products. A similar phenomenon has been observed for type-2 diabetes and coronary heart disease," wrote the researchers.
"It is postulated that saturated fats in high-fat dairy products may mitigate the beneficial effects of other components of dairy products, including calcium," they added.
When the researchers considered calcium, they stated that previous studies have reported that the mineral "may lower the activity of renin-angiotensin system, improve sodium-potassium balance, and inhibit vascular smooth muscle cell (VSMC) constriction.
"High calcium intake facilitates weight loss and enhances insulin sensitivity, which also contribute to BP reduction," they added.
The implications of the research could be accentuated by recent findings published in the Archives of Internal Medicine that stated Americans are ignoring the DASH (Dietary Approaches to Stop Hypertension) Diet.
The Harvard researchers noted several limitations with their study, including the using data from only one FFQ per subject, which might not capture accurately changes in diet after the measurement. They also stress that the results only apply to white health professional women and therefore generalisations to other populations is not possible.
Volume 51, Pages 1-7, doi:10.1161/HYPERTENSIONAHA.107.107821
"Dietary Intake of Dairy Products, Calcium, and Vitamin D and the Risk of Hypertension in Middle-Aged and Older Women"
Authors: L. Wang, J.E. Manson, J.E. Buring, I.-M. Lee, H.D. Sesso