Date: Published online February 7, 2008
Summary: Eating low-fat foods and dairy products high in calcium and vitamin D decreased the risk of developing high blood pressure and heart disease in a large group of middle-aged and older women. However, taking calcium and vitamin D supplements did not affect the risk of high blood pressure or heart disease.
Why it’s important: Only limited information exists on the association between dairy products, calcium and vitamin D and high blood pressure and very few of these studies have been prospective in nature ie a study in which the subjects are identified and then followed over a period of time. This prospective study involving nearly 30,000 women over age 45 provides definitive information on the effects of dairy products, and the calcium and vitamin D they contain, on blood pressure. It also evaluates the effects of calcium and vitamin D supplements. The effects of diet on blood pressure could have major public health implications. Blood pressure remains a major public health problem in the
What’s already known: Previous studies have suggested that the more dairy products people eat, the lower their risk for developing metabolic syndrome (a group of metabolic risk factors in one person), type 2 diabetes and heart disease. The effect is thought to result from calcium and other nutrients found in dairy products. Scientists believe that high intake of calcium reduces the levels of specific hormones and antioxidants. That may reduce the amount of calcium that goes into cells. When that happens, more fat is metabolized in the cell and less fat is generated by cells. Vitamin D is critical for the absorption of calcium and the metabolism of the two are interrelated. Studies of high blood pressure and dairy products in children, young adults and adults in Mediterranean countries indicate that higher amounts of dairy products and lower blood pressure are related. The federally funded Dietary Approach to Stop Hypertension (DASH) study showed that diets rich in fruits, vegetables and low-fat dairy products with low total and saturated (animal product) fats reduced blood pressure in people who had and who did not have high blood pressure compared to a diet that was rich in fruit and vegetables alone.
How this study was done: This study used data collected from the Women’s Health Study, which was designed to find out whether taking low-dose aspirin and vitamin E could lower the risk of developing heart disease and cancer. As part of the study, the women aged 45 and above filled out a 131-item questionnaire about the food they ate. The researchers included women in the study who answered the questions completely and had no sign of high blood pressure or heart disease. They analyzed information from 28,886 women and calculated how much of each food item the women ate daily, including dairy products. They also found out which women took supplements or pills containing calcium and vitamin D. During the 10 years of the study, the researchers identified women who developed high blood pressure. They then ranked the women by the amount of dairy products they reported eating.
What was found: Over 10 years, 8,710 women developed high blood pressure. The more dairy products and food containing vitamin D the women ate, the lower their risk of developing high blood pressure. The researchers found that women who drank two or more servings of fat-free milk or low-fat dairy products daily reduced their high blood pressure risk by 10 percent compared to women who consumed the low-fat dairy products less than once a month. However, the study showed no benefit from taking supplements containing calcium or vitamin D. Higher-fat dairy products did not protect the women from high blood pressure, but they did not increase their risk either.
The researchers, led by Lu Wang, M.D., Ph.D., of the division of preventive medicine at Brigham and Women’s Hospital in Boston, wrote: “Because dairy products account for nearly 80 percent of total calcium intake in the American diet, our findings on total dietary calcium suggested a major role of this nutrient in mediating the beneficial effects of dairy products in the prevention of hypertension. Milk fortified with vitamin D is the main source of vitamin D intake in the American diet.” However, they also wrote: “It remains unclear why benefits are observed for low-fat dairy products but not for high-fat dairy products.” They think that the saturated fats found in these products weigh against the beneficiary factors that reduce blood pressure.
The study is limited. The eating habits of the women were measured only once – at the start of the study. Also, the researchers only found out if women developed high blood pressure during the study period if the women reported it. Although the researchers do not think that the women’s lower blood pressure risk was associated with an overall better eating pattern, they couldn’t rule it out. The women in the study were mostly white and professionals, which could affect the findings.
The bottom line: Drinking a glass of fat-free milk or eating other low-fat dairy products could lower your blood pressure somewhat. Taking supplements containing calcium and vitamin D probably will not.
Journal: Hypertension
Journal citation: Hypertension. 2008;51:1-7
This content is reviewed regularly. Last updated 03/28/08.
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http://www.americanheart.org/presenter.jhtml?identifier=3055292
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