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Cardiovascular Disease

The evidence to date does not support an association between milk product consumption and an increased risk of cardiovascular disease.

Synopsis

In fact, emerging evidence suggests that milk products may play a role in the prevention of heart disease and stroke. Although the exact mechanisms by which milk products may confer a benefit have yet to be clarified, there is very good evidence linking milk product consumption to the prevention and management of hypertension, metabolic syndrome, type 2 diabetes and obesity, all of which are key cardiovascular disease risk factors. Several aspects of milk products may play a role, including their low glycemic index and the following components:

  • Calcium,
  • Vitamin D,
  • Vitamin K2,
  • Bioactive peptides.

The Evidence

A systematic review with meta-analysis of 15 prospective cohort studies with over 600,000 subjects revealed that there was an overall reduction of about 10% to 15% in the incidence of heart disease in subjects who had reported drinking the most milk relative to those consuming the least milk.1 In addition, the overall risk of myocardial infarction associated with milk consumption from 4 case-control studies was 0.83. Whole milk was the type of milk consumed in the majority of the studies reviewed.1

A review of the evidence from the proceedings of a scientific symposium on the role of milk products, particularly dairy fat, in cardiovascular disease indicated that there is no clear evidence that milk product consumption is consistently associated with an increased risk of cardiovascular disease.2 Some of the key findings from this symposium are listed below:

  • While higher-fat milk products contain saturated fat, the evidence from prospective cohort studies does not consistently demonstrate a direct relationship between the intake of milk products and the risk of cardiovascular disease;
  • Some studies have shown that fermented milk products, most notably yogurt, lower plasma LDL cholesterol levels, but more studies are needed in order to draw firm conclusions;
  • One of the established properties of milk fat compared to polyunsaturated oils is that milk fat increases the plasma concentration of HDL cholesterol, which is protective;
  • Data from clinical trials and epidemiological studies do not support an independent role of saturated fat with respect to cardiovascular disease risk;
  • Emerging studies indicate a role of milk product consumption in the suppression of inflammation and oxidative stress, which are recognized as key etiological factors in the development of atherosclerosis and cardiovascular disease.

Another systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease also indicated that there is no significant association with an increased risk of coronary heart disease and the following elements3:

  • Saturated fat,
  • Total fat,
  • Meat,
  • Eggs,
  • Milk products.

Other key findings from this study include:

  • No association between a Western dietary pattern and coronary heart disease;
  • A strong association between a Mediterranean dietary pattern (includes cheese and yogurt) and a lower risk of coronary heart disease;
  • Strong evidence for several protective factors (vegetables, nuts and a Mediterranean diet) on coronary heart disease;
  • Strong evidence for harmful factors such as trans fatty acids and high glycemic index foods on coronary heart disease.

The authors of another systematic review of 10 prospective cohort studies that evaluated the role of milk consumption or the intake of calcium from dairy sources with heart disease and stroke as the primary outcomes concluded that milk consumption is associated with a small but worthwhile reduction in heart disease and stroke.4 A pooled estimate of the relative odds for subjects in the highest levels compared to lowest levels of milk consumption is 0.87 for ischaemic heart disease and 0.83 for ischaemic stroke. The odds ratio for any vascular event is 0.84.4

The Caerphilly cohort study, a prospective study of 2,512 men from South Wales (aged 45 to 59 years at recruitment and who were followed for 20 to 24 years) showed that consumption of milk products was not associated with an increased risk of vascular disease.5 Data from a sub-sample of these participants (n = 665) using 7-day weighed food records (a more reliable method for estimating food intake) also confirmed that there was no evidence for an association with milk product consumption and increased risk of vascular disease. Furthermore, those whose consumption of milk was at the median amount or higher had a significantly reduced risk of an ischaemic stroke and possibly a reduced risk of an ischaemic heart disease event.6

A prospective cohort study of 5,765 men from West Scotland aged 35 to 64 years at baseline that examined the association between milk intake and coronary heart disease and mortality found no evidence to suggest that men who consumed full-fat milk each day were at increased risk of death from all causes or death from coronary heart disease.7

On the other hand, data from the Nurses’ Health Study, a prospective cohort study of 121,700 female nurses, indicated that consumption of whole milk was significantly associated with an increased risk of coronary heart disease, while the consumption of skim milk was associated with a decreased risk.8

The landmark randomized controlled Dietary Approaches to Stop Hypertension (DASH) Diet Study, which demonstrated a significant and substantial reduction in blood pressure when an adequate intake of milk products (including some higher-fat milk products such as cheese) was included as part of a healthy dietary pattern,9 also showed a significant reduction in serum homocysteine levels, an independent risk factor for heart disease,10 as well as reductions in total and LDL cholesterol levels.11 Reductions in blood pressure of the magnitude achieved by the DASH diet could translate into a 15% reduction in ischaemic heart disease and a 27% reduction in stroke.9

A prospective cohort study, published in 2009, which consisted of 36,019 women, part of the Swedish Mammography Cohort demonstrated that consistency with the DASH diet significantly reduced the risk of heart failure. Indeed, after adjustment of potential confounders, those in the top quartiles with respect to consistency in following the DASH diet had a 37% lower incidence of heart failure compared to those in the bottom quartiles (ptrend < 0,001).12

Potential Mechanisms

The mechanisms by which milk products may modulate the risk for cardiovascular disease remain unclear, but several of their aspects and components may be involved. Calcium may play a role via its impact on hypertension, weight, fat mass and blood lipid levels.13

By virtue of their low glycemic index, milk products may be protective. High glycemic index foods have been shown to have a strong association with an increased risk for cardiovascular disease.3

Emerging evidence also indicates that milk products may suppress inflammation and oxidative stress, two processes believed to be key etiological factors in the development of cardiovascular disease.2

New evidence also reveals that high intakes of vitamin K2 (menaquinone) found in fermented products such as cheese may be protective against the development of coronary heart disease.14

Cheese may also be protective due to its overall positive effect on serum lipids, particularly HDL cholesterol.15,16

Conclusions

There is very good evidence to date to at least support the lack of an association between increased milk product consumption and an increased risk for cardiovascular disease.

In fact, there is good emerging evidence that adequate milk product consumption, including intakes of higher-fat milk products such as cheese, may decrease the risk for cardiovascular disease. Moreover, there are high-quality studies to support a beneficial role of milk products in several cardiovascular disease risk factors, such as hypertension, metabolic syndrome, type 2 diabetes and obesity.

More studies are needed with respect to the role of milk products on cardiovascular disease outcomes such as myocardial infarction, ischemic heart disease and mortality, especially the role of high- versus low-fat products as well as individual products such as yogurt and cheese.

References

  1. Elwood PC et al. The survival advantage of milk and dairy consumption: an overview of evidence from cohort studies of vascular diseases, diabetes and cancer. J Am Coll Nutr 2008;27(6):723S-734S.
  2. German JB et al. A reappraisal of the impact of dairy foods and milk fat on cardiovascular disease risk. Eur J Nutr 2009;DOI: 10.1007/s00394-009-0002-5
  3. Mente A et al. A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease. Arch Intern Med 2009;169(7):659-669.
  4. Elwood PC et al. Milk drinking, ischaemic heart disease and ischaemic stroke II. Evidence from cohort studies. Eur J Clin Nutr 2004;58(5):718-724.
  5. Elwood PC et al. Milk drinking, ischaemic heart disease and ischaemic stroke I. Evidence from the Caerphilly cohort. Eur J of Clin Nutr 2004;58(5):711-717.
  6. Elwood PC et al. Milk consumption, stroke and heart attack risk: evidence from the Caerphilly cohort of older men. J Epidemiol Community Health 2005;59:502-505.
  7. Ness AR et al. Milk, coronary heart disease and mortality. J Epidemiol Community Health 2001;55(6):379-382.
  8. Hu FB et al. Dietary saturated fats and their food sources in relation to the risk of coronary heart disease in women. Am J Clin Nutr 1999;70(6):1001-1008.
  9. Appel LJ et al. A clinical trial of the effects of dietary patterns on blood pressure. N Engl J Med 1997;336(16):1117-1124.
  10. Appel LJ et al. Effect of dietary patterns on serum homocysteine: results of a randomized, controlled feeding study. Circulation 2000;102(8):852-857.
  11. Obarzanek E et al. Effects on blood lipids of a blood pressure-lowering diet: the Dietary Approaches to Stop Hypertension (DASH) Trial. Am J Clin Nutr 2001;74(1):80-89.
  12. Levitan EB et al. Consistency with the DASH diet and incidence of heart failure. Arch Int Med 2009;169(9):851-857.
  13. van Meijl LE et al. Dairy product consumption and the metabolic syndrome. Nutr Res Rev 2008;21(2):148-157.
  14. Gast GC et al. A high menaquinone reduces the incidence of coronary heart disease in women. Nut Metab Cardiovasc Dis 2008;doi:10.1016/j.numecd.2008.10.004.
  15. Hostmark AT et al. Serum HDL cholesterol was positively associated with cheese intake in the Oslo Health Study. J Food Lipids 2009;16(1):89-102.
  16. Houston DK et al. The association between cheese consumption and cardiovascular risk factors among adults. J Hum Nutr Diet 2008;21(2):129-140.

Keywords: cardiovascular disease, blood pressure

Scientific Evidence Keywords

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