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Hypertension: Summary of Evidence

Introduction

Evidence from emerging studies indicates that the consumption of milk products has a beneficial effect on blood pressure. Hypertension Canada recommends the DASH diet for the prevention and management of high blood pressure in at-risk individuals. The potential mechanisms by which milk products may modulate blood pressure need to be elucidated, but there is evidence that several components of milk products may be involved, including:

• Calcium,
• Vitamin D,
• Magnesium,
• Potassium,
• Phosphorous,
• Bioactive peptides.

The Evidence

A 2011 systematic review and meta-analysis, which included about 45,000 men and women and involved 2 to 15 years of follow-up, examined the association between total dairy, low- and high-fat dairy, cheese, and fluid dairy (milk and yogurt) and the development of elevated blood pressure during adulthood. It was found that there is an inverse association with the consumption of low-fat and fluid (milk and yogurt, low and high fat) milk products and the risk of elevated blood pressure.¹

• The consumption of total dairy foods (low and high fat) for the highest compared with the lowest intake category was associated with a significantly reduced risk of elevated blood pressure, with a relative risk of 0.87 (95% CI: 0.81-0.94), representing a 13% risk reduction;
• There was a significant association between the consumption of low-fat milk products and a reduced risk of elevated blood pressure, with a relative risk of 0.84 (95% CI: 0.74-0.95);
• There was no association between the high consumption of high-fat milk products and the risk of elevated blood pressure, with a relative risk of 1.00 (95% CI: 0.89-1.11);
• There was no association between the consumption of cheese and the risk of hypertension, with relative risk of 1.00 (95% CI: 0.89-1.12);
• The consumption of fluid milk products (milk and yogurt, low or full fat) was significantly associated with a reduction in the development of elevated blood pressure, with a relative risk of 0.92 (95% CI: 0.87-0.98).

A 2009 prospective cohort study conducted in a population of older Dutch individuals examined the relation between milk product intake and incident hypertension in 2,245 men and women (55 years or older) who were free of hypertension at baseline. Risk of hypertension was significantly inversely associated with milk product intake.²

• The median energy-adjusted intake of total milk products for the study population was 396 g/day, ranging from 164 g/day (1 serving/day) in the lowest quartile to 691 g/day (4.5 servings/day) in the highest quartile;
• Low-fat milk (31%), buttermilk (17%), high-fat milk (10%), low-fat yogurt (9%), and Gouda cheese (7%) made the largest contribution to the total milk product intake;
• After adjustment for confounders, there was a significant 24% reduction in risk for total milk product intake between the highest and lowest quartiles of intake;
• Each serving-per-day increase in total milk product intake (defined as 150 mL) was associated with a 7% lower risk of hypertension;
• There was a significant 31% reduction in risk between the highest and lowest quartiles of low-fat milk product consumption;
• There was no significant association with high-fat milk products or cheese;
• After 6 years of follow-up, the associations with hypertension were attenuated to risk reductions of 20% for both total and low-fat milk products between the extreme quartiles of intake. The association between milk product intake and hypertension did not significantly vary by sex.

Another prospective cohort study of 28,866 US women aged 45 years or more examined associations between intakes of milk products, calcium, and vitamin D and incident hypertension over 10 years of follow-up.³

• After adjusting for major hypertension risk factors, the relative risk for the highest compared to the lowest quintile of low-fat milk product intake was 0.89 (p_trend = 0.001);
• After adjustment, the relative risk across quintiles of higher-fat milk products was 0.97 (p_trend= 0.17);
• The risk of hypertension decreased in the higher quintile of dietary calcium and vitamin D (0.87 and 0.95, respectively), but did not change with calcium and vitamin D supplements.

In another prospective cohort study conducted in Spain of 5,880 university graduates over the age of 20 who were free of hypertension and cardiovascular disease at baseline and who were followed for a median duration of 27 months, the intake of low-fat milk products was associated with a significant reduction in the risk of developing hypertension.⁴

• There was a significant 54% reduction in risk between the highest and lowest quintiles of low-fat milk product consumption after adjustment of potential confounding factors, including known risk factors for hypertension and other dietary variables;
• There was a significant trend that suggested a dose-response relation;
• There was no association with higher-fat milk products and hypertension.

In the landmark randomized controlled Dietary Approaches to Stop Hypertension (DASH) Diet Study, the impact of dietary patterns on blood pressure was examined. After following a control diet for 3 weeks, 459 adults were randomized to 1 of 3 diets as follows:^5-6

• Control diet;
• Fruits and vegetables diet: 8 to 10 servings/day;
• Combination diet (DASH): close to 3 servings of milk products, including about 1 oz of regular-fat cheese, in addition to the 8 to 10 servings of fruits and vegetables per day.

Within 2 weeks, both intervention diets significantly lowered blood pressure, with similar reduction patterns observed in men and women and in minorities and non-minorities.

• The dairy-enriched combination diet (DASH diet) had twice the impact of the fruits and vegetables diet, reducing systolic blood pressure by 5.5 mm Hg and diastolic blood pressure by 3.0 mm Hg (p < 0.001) more than the control diet;
• About 50% of the magnitude in these reductions could be ascribed to the milk products per se in the diet;⁶
• Among hypertensive subjects, the combination diet reduced systolic blood pressure and diastolic blood pressure by 11.4 and 5.5 mm Hg more than the control diet, respectively (p < 0.001), making this diet a viable alternative to monotherapy for mild hypertension;
• Since weight and sodium intake (3,000 mg) were held constant and alcohol intake was similar in all 3 groups, these well-known confounders did not account for the observed reductions in blood pressure;
• Reductions in blood pressure of the magnitude achieved by the DASH diet—which is rich in milk products, fruits and vegetables—could translate into a 15% reduction in ischemic heart disease and a 27% reduction in stroke.⁵

Moreover, Hypertension Canada recommends the DASH diet for the prevention and management of hypertension in hypertensive and normotensive individuals at increased risk.⁸ Similarly, in their guidelines for the year 2000, the American Heart Association also recommended the DASH diet for heart health.⁹ In its 2007 evidence-based guidelines for cardiovascular-disease prevention in women, the American Heart Association also recommends an increased consumption of low-fat milk products for optimal blood pressure.¹⁰

Potential Mechanisms

Although the mechanisms by which milk products may modulate blood pressure remain to be fully elucidated, calcium is thought to be one of the main nutrients responsible for the impact of milk products on blood pressure control.⁷

Other minerals in milk products, such as magnesium and potassium, may also regulate blood pressure, but their individual contribution is difficult to isolate as they are often found in foods rich in calcium.⁷

As well, both casein and whey protein (the main proteins in milk products) contain specific bioactive peptides that have been shown to have an angiotensin-1-converting enzyme (ACE) inhibitory effect, a key process in blood pressure control.⁷

Other studies have shown that certain milk-derived peptide combinations also have hypotensive effects via the modulation of endothelin-1 release by endothelial cells.⁷ A meta-analysis of milk tripeptides on blood pressure indicated that milk-derived tripeptides have hypotensive effects in prehypertensive and hypertensive individuals.¹¹

Conclusions

There is consistent and strong evidence to support a causal relation between milk product consumption and blood pressure control.

The evidence to date indicates that total intake of milk products, especially of lower-fat and higher-fat milk and yogurt, may have a protective role against hypertension.

There appears to be no association between high-fat milk products and cheese and risk of hypertension.

More studies, including randomized controlled trials and mechanistic studies, are needed to provide definitive answers on the role of milk products in the prevention and management of hypertension.

Keywords: hypertension, blood pressure, dash diet, sodium, canadian hypertension society, american heart association

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