PURE: Higher Dairy Consumption Tied to Lower CVD, Mortality

Batya Swift Yasgur, MA, LSW

September 14, 2018

Consuming two or more servings of whole-fat dairy products per day is associated with lower rates of cardiovascular disease (CVD) and mortality compared with less dairy consumption or consumption of lower-fat dairy products, new research suggests.

Investigators analyzed data from over 136,000 adults in 21 countries in the ongoing Population Urban Rural Epidemiology (PURE) study, following participants for an average of 9 years.

Compared with a dairy-free diet, consumption of two or more servings of total dairy per day was associated with significant reductions in the risks for major CVD and total mortality combined. The risk for stroke was over twice as high in individuals who did not consume dairy products.

Whole-fat dairy was also associated with lower rates of mortality and CVD compared with lower-fat dairy, with milk and yogurt found to be the dairy products associated with the most benefit.

"We observed that higher dairy consumption was associated with lower risks of mortality and CVD, particularly stroke," lead author, Mahshid Dehghan, MSc, PhD, investigator, Nutrition Epidemiology Program, Population Health Research Institute, and senior research associate, Department of Medicine McMaster University, Hamilton, Ontario, Canada, told theheart.org | Medscape Cardiology.

"Our study suggests that consumption of dairy products should not be discouraged and perhaps even be encouraged in low- and middle-income countries where dairy consumption is low," she said.

The study was published online September 11 in The Lancet.

Adverse and Beneficial Effects

CVD is "the leading cause of mortality worldwide, with 80% of the burden in low-income and middle-income countries," the authors write.

Dietary guidelines have recommended minimizing consumption of whole-fat dairy products for CVD prevention because these saturated fats have been "presumed to adversely affect blood lipids and increased cardiovascular disease and mortality."

However, dairy products also have benefits, Dehghan explained, noting that they contain a range of potentially beneficial compounds, including specific amino acids, medium- and odd-chain saturated fats, natural trans fats, vitamin K1 and K2, and calcium.

Additionally, dairy products can be fermented or contain probiotics, "many of which may also affect health outcomes," she pointed out.

The impact of dairy may not therefore be reliably determined exclusively by its effect on a single risk marker, such as low-density lipoprotein cholesterol or fatty acids.

Previous studies have demonstrated positive effects of dairy products, but most have been conducted in North America and Europe, where dairy consumption and intake of saturated fatty acids are more common than in other regions of the world, and where coronary heart disease (CHD) surpasses stroke. By contrast, strokes are more common than CHD in other areas, such as East Asia and Africa.

"Therefore, data from all world regions are essential to making global policy recommendations," the authors state.

To investigate the question, the researchers used data from the first and second phases of the study, including 136,384 individuals (aged 35 - 70 years) from 21 countries.

Data were collected at the community, household, and individual levels using standardized questionnaires, and standard case-report forms were used to record data for major cardiovascular events and mortality during the follow-up period (a median of 9.1 years [interquartile range, 6.4 - 9.9 years]).

Country-specific habitual food intake was recorded at baseline for each participant using validated food-frequency questionnaires (FFQs).

Participants were asked how often, on average, they had consumed specific foods or drinks during the past year, with standard serving sizes assigned to each food item.

The reported frequency of consumption for each food item was then converted to daily intake and multiplied by serving size.

Dairy products comprised milk, yogurt, a variety of cheeses, yogurt drinks, and mixed dishes prepared with dairy, which were disaggregated into their constituents. A proportional weight was then assigned to each component and then included in the related dairy group.

Products were further grouped into whole- and low-fat dairy products.

One standard serving of dairy was equivalent to a glass of milk (244 g), a cup of yogurt (244 g), one slice of cheese (15 g), and one teaspoon of butter (5 g).

The primary outcome was the composite of mortality or major cardiovascular events (ie, death from cardiovascular causes, nonfatal myocardial infarction [MI], stroke, or heart failure).

Other outcomes were total mortality and major CVD (fatal and nonfatal MI, fatal and nonfatal strokes, heart failure, and cardiovascular mortality).

Participants were grouped into four categories: no dairy (n = 28,674), less than 1 serving per day (n = 55,651), 1 to 2 servings per day (n = 24,423), and more than 2 servings per day (n = 27,636).

Consistency of Findings

During the follow-up, 10,567 (7.7%) individuals either died (n = 6796) or had major cardiovascular events (n = 5855).

Countries with higher dairy intake were located in Europe and North America, the Middle East, and South America. The highest yogurt intake was in the Middle East, Europe and North America, and South Asia, and the highest intake of cheese was in Europe, North America, and the Middle East. The highest amount of butter was consumed in South America, Europe, North America, and the Middle East, but the mean level of intake was modest.

Compared with no intake, high intake of total dairy (more than 2  servings per day; mean intake, 3.2 servings) was associated with a lower risk for the composite outcome, total mortality, noncardiovascular mortality, cardiovascular mortality, major CVD, and stroke. There was no significant association with MI, they note.  

Table. PURE: Outcomes by Dairy Intake

Endpoint No Dairy Intake (%) High Dairy Intake (>2 Servings/Day) (%) Hazard Ratio (95% Confidence Interval) P Value for Trend
Composite outcome 8.7 6.6 0.84 (0.75 - 0.94) .0004
Total mortality 5.6 3.4 0.83 (0.72 - 0.96) .0052
Noncardiovascular mortality 4.0 2.5 0.86 (0.72 - 1.02) .046
Cardiovascular mortality 1.6 0.9 0.77 (0.58 - 1.01) .029
Major CVD 4.9 3.5 0.78 (0.67 - 0.90) .0001
Stroke 2.9 1.2 0.66 (0.53 - 0.82) .0003
MI 1.6 1.9 0.89 (0.71 - 1.11) .163
Heart failure 0.3 0.5 1.06 (0.71 - 1.57) .90

 

More than one serving per day vs no intake of milk and yogurt was associated with lower risk for the composite outcome, but there was no significant association for cheese, they note. Butter intake was low and was not significantly associated with clinical outcomes.

High intake of total dairy vs low intake, defined as more than 2 servings per day vs less than 0.5 servings per day was associated with lower risk of the composite outcome, total mortality, and major CVD.

High intake vs low intake of only whole-fat dairy products was associated with a lower risk for the composite outcome, total mortality, and major CVD.

The results were consistent across regions with low dairy or high dairy intake but strongest in regions with lower mean intakes of dairy foods (ie, China, South Asia, Southeast Asia, and Africa).

"We adjusted for established and potential risk factors of mortality and CVD, as well as for other dietary variables, but, as with any observational study, residual confounding is a possibility," Dehghan commented.

Changes to Current Practice Premature

Coauthor of a related editorial, Jimmy Chun Yu Louie, BSc, MNutrDiet, PhD, APD, assistant professor in food and nutritional science, School of Biological Sciences, University of Hong Kong,  told theheart.org | Medscape Cardiology that the study's strengths include the large sample size from a variety of countries in five regions, the use of validated FFQs, and appropriate adjustments to known confounders.

Nevertheless, clinicians should encourage patients to eat only more low-/reduced-fat dairy and should "stick to current guidelines" because more research is needed to specifically test whether whole-fat dairy is indeed more protective than reduced-fat dairy, he cautioned.

Additionally, the study measured dairy consumption only at baseline, which does not take into account changes in lifestyle and consumption over time or economic growth in areas such as India and China.

Moreover, a partial explanation for the findings is that those who consume more dairy products may be more health-conscious or well-off socioeconomically, both of which are confounders for CVD outcomes — although some confounding effects were accounted for in the multivariate adjusted models, he said.

Dehghan added, "The consistency of results across regions with markedly different lifestyles makes it less likely that confounders, which are likely to vary in different regions, explain our observations."

Asked for comment, Jo Ann Carson, PhD, past chair of the American Heart Association's Nutrition Committee, called the findings "interesting."

"The American Heart Association currently recommends fat-free and low-fat dairy products as part of a healthy eating pattern that also emphasizes a variety of fruits and vegetables, whole grains, skinless poultry and fish, nuts and legumes and non-tropical vegetable oils," she told theheart.org  | Medscape Cardiology in an emailed comment.  

"This is interesting research to add to the body of literature on dairy and its usefulness in preventing cardiovascular disease in low- and middle-income countries," she added. "What's important for US clinicians to remember is that the current guideline on dairy to prevent cardiovascular disease remains unchanged: people should choose low-fat and skim (fat-free) dairy products whenever possible in the context of an overall heart healthy dietary pattern."

The PURE study is an investigator-led study funded by the Population Health Research Institute, the Canadian Institutes of Health Research, Heart and Stroke Foundation of Ontario, and Canadian Institutes of Health Research's Strategy for Patient Oriented Research, through the Ontario SPOR Support Unit, and the European Research Council. Additional sources of funding are listed on the original paper. The study authors have disclosed no relevant financial relationships. Louie reports funding for projects by Dairy Australia and was sponsored to present the findings of the projects at an Australian national conference. His coauthors' disclosures are listed on the original paper.

Lancet. Published online September 11, 2018.  Abstract, Editorial

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