Dairy and Hypertension
Increased consumption of low-fat dairy foods are recommended
In view of the high prevalence and major implications of hypertension, attempts to decrease blood pressure are justified. A large evidence base has confirmed an association between consumption of dairy products and reductions in blood pressure. The beneficial effect of dairy consumption on blood pressure appears to be derived from the complete nutritional profile of dairy products and not solely from calcium. The combination of minerals, vitamins, proteins and essential fatty acids, as well as the specific peptide sequences of dairy contribute to this effect. Fatfree and low fat dairy products, especially milk, appear to have an even more significant lowering effect on blood pressure than other dairy products. Although pharmacological treatment of hypertension is effective in many patients, it might be inconvenient, expensive and accompanied with adverse effects in others. Based on the evidence, increased consumption of lowfat dairy foods are recommended in an effort to prevent hypertension or reduce blood pressure.
The most wellknown randomised controlled trial related to diet and hypertension is the DASH trial, which showed that dietary interventions can effectively impact on blood pressure, to the same extent or more as singledrug therapy. A diet rich in fruit, vegetables and low-fat dairy products combined with lower intakes of total and saturated fats over a period of eight weeks, resulted in a significant decrease in blood pressure compared with that of subjects on a typical American control diet (5.5 mmHg systolic blood pressure and 3.0 mmHg diastolic blood pressure). In South Africa, a study by Charlton et al., conducted amongst 325 men and women from three different ethnic groups in Cape Town, found that dietary calcium intake was inversely associated with both systolic and diastolic blood pressure. A systematic review by McGrane et al. covered recent, randomised controlled trials and cohort studies. The authors found significant inverse associations with hypertension for high versus low intake of total dairy, lowfat dairy, and fluid dairy foods. Ralston et al. undertook a metaanalysis of five cohort studies involving nearly 45 000 subjects of which 11 500 had elevated blood pressure. Their analysis showed significant inverse associations of total dairy, lowfat dairy and fluid dairy foods (milk and yoghurt) with blood pressure. SoedamahMuthu et al., performed a doseresponse metaanalysis of prospective cohort studies evaluating dairy intake and risk of hypertension in 57 256 subjects (of which 15 367 were hypertensive) who were followed up for between two and 15 years. In their analysis, total dairy, lowfat dairy and milk were all linearly associated with a lower risk of hypertension.
The association between dairy products and blood pressure is stronger than the association between calcium intake and blood pressure, suggesting that other components in dairy products also play a role in this association. Dairy products are usually low in sodium (cheese excluded) and rich in protein, minerals (calcium, magnesium, potassium and phosphorus), vitamins (cobalamin and riboflavin), and trace elements (iodine, selenium and zinc), which may reduce blood pressure individually or in combination. The blood pressure lowering effects of single nutrients may be too small to detect in primary clinical trials, but when consumed together, their combined effect may be sufficient to be detected and provide protective effects. It is also possible that there may also be some unrecognised ingredients in dairy products that may affect blood pressure. The bioactive milk peptides in dairy, such as lactotripeptides, may also contribute to the protective effect of dairy on blood pressure. These bioactive peptides are released from dairy products after fermentation during food processing or digestion in the small intestine and are hypothesised to inhibit the action of angiotensin 1converting enzyme (ACE), and in so doing prevent blood vessel constriction. ACE is a key participant in the reninangiotensin system, which is a primary regulator of blood pressure and fluid and electrolyte balance in the body. ACE converts inactive angiotensin I to angiotensin II, which increases blood pressure by constricting vascular smooth muscle. ACE inhibition lowers the production of angiotensin II, which inhibits the release of aldosterone (which conserves sodium, increases potassium loss and increases water retention) and so decreases blood pressure.
The benefits of lowfat dairy consumption on blood pressure justify recommendations to increase consumption of these foods.