Cardiovascular disease

 

The focus on dairy foods and cardiovascular disease (CVD) is often in relation to saturated fat. There is an assumption that because some dairy foods contain saturated fatty acids and dairy in general contributes to saturated fat intake in the diet, that it also increases the risk of cardiovascular disease. Yet the majority of epidemiological studies have shown no adverse effects of regularly consuming milk and dairy foods such as yogurt and cheese on cardiovascular health, irrespective of fat content. In fact, in some cases a cardio-protective effect has been observed.

The explanation for this may lie in the complex composition of milk and dairy foods which, in addition to saturated fat, contain other nutrients and bioactive components such as calcium, potassium and bioactive peptides in the dairy matrix which may be beneficial to cardiovascular health. In addition, the overall fatty acid profile of milk and dairy may not have the detrimental effect on blood lipids or other cardiovascular parameters that has been assumed.

In the absence of long-term intervention trials, the best available data on the relationship between dairy foods and cardiovascular disease are from large, long-term observational studies. There are several studies of this type in European populations. For example, a prospective cohort study from the UK reports that men who drank the most milk (around a pint / 586ml of whole milk a day) had fewer heart attacks and fewer strokes than those who had little or no milk in their diets1. The very large Netherlands Cohort Study, consisting of over 120,000 men and women, showed no association between total milk product consumption and stroke mortality, although butter and dairy fat was associated with a small (7%) increased risk of all-cause and heart disease mortality among women2. Recent data from the smaller Dutch Hoorn Study also found that overall dairy intake was not associated with CVD mortality but the intake of high-fat dairy products was3. In contrast, the Rotterdam Study reports that in an older Dutch population, high-fat dairy was associated with a reduced risk of fatal stroke; total dairy consumption or the intake of specific dairy products was not related to CVD events4.

In another Dutch prospective cohort, there was again no evidence that dairy products increased risk of heart disease or stroke5. In fact, high intakes of total and low-fat dairy were associated with a lower coronary heart disease (CHD) risk in participants without hypertension. Low-fat dairy consumption was also associated with reduced risk of stroke in cohorts of Swedish men and women6. In the same cohorts, a high intake of fermented milk (yogurt and cultured sour milk) was found to reduce CVD risk7. Fermented milk and cheese were also associated with reduced cardiovascular disease mortality8. There was, however, an increased CVD mortality risk reported in this study in those drinking three or more glasses of (non-fermented) milk a day compared with less than one glass. The reason for this discrepancy in the same cohort is not clear and the authors urge a cautious interpretation of the results. Moreover, when these data were re-examined, milk consumption was associated with a lower risk of CVD mortality9. In line with the majority of epidemiological studies, a recent Danish investigation reports no adverse effects of dairy on cardiovascular health10. The French MONICA project conducted over 14 years, found that dairy consumption (particularly milk intake) as part of a diverse, healthy diet was associated with the lowest mortality rate mostly due to reduced cardiovascular deaths11.

Meta-analyses for milk

A number of analyses have pooled the data from individual prospective studies such as these and their results strengthen the evidence that regularly consuming milk and other dairy products does not increase risk of cardiovascular disease and may even have a protective effect1,13-20. In relation to milk, an overview conducted in 2010 concluded that milk drinking is not harmful and may be associated with a small but worthwhile reduction in risk of coronary heart disease (8%) and a more substantial reduction in stroke risk (21%) for those who drank the most milk compared with those who drank the least13. The pooled results of seventeen studies in 2011 also found milk intake was associated with a small potential reduction in overall cardiovascular risk of 6% for each 200ml of milk consumed a day14. This analysis found no association between high intakes of either regular-fat or low-fat dairy products and increased risk of death from cardiovascular disease. Similarly, systematic reviews in 2015 and 2017 examining milk consumption and cardiovascular disease mortality observed no consistent association15,16. This was also the conclusion for milk and CVD risk in a meta-analysis published in 2016; milk intake was found to be neutral with respect to risk of stroke and coronary artery disease17.

Meta-analyses for dairy products 

Meta-analyses also support neutral or beneficial effects of other dairy foods on cardiovascular disease. Twenty two prospective cohort studies were included in an analysis published in 2015 which examined stroke and CHD incidence in relation to intake of individual dairy foods, and to low- and regular-fat dairy18. Cheese consumption was associated with a 16% decreased heart disease risk, and both cheese and low-fat dairy foods were associated with reduced risk of stroke (9% and 7% respectively). An earlier meta-analysis in 2014 looking specifically at stroke also reported similar reductions in risk with low-fat dairy (9%) and cheese intake (6%) and, in addition, with total dairy (12%) and fermented milk (20%)19. Similarly, in another meta-analysis including 18 studies which had examined dairy intake and stroke risk, milk and cheese consumption were associated with reduced risk of stroke; risk reductions were maximal around 125g/day for milk (16%) and from 25 g/day upwards for cheese (9%)20. Cheese was also associated with a lower risk of stroke (13%) in a meta-analysis published in 2016, as was total dairy intake (9%)21. In addition, cheese intake was associated with an 18% reduced risk of coronary heart disease. A beneficial effect of cheese was also supported by a meta-analysis of prospective cohort studies published in 2017 in which cheese intake was associated with 10%, 14% and 10% reduced risks of total CVD, CHD and stroke respectively22. A recent systematic review of the association between dairy product consumption and risk of various cardiovascular-related clinical outcomes also reports favourable associations between intakes of total dairy, low-fat dairy, cheese, and fermented dairy and the risk of stroke17. Similarly, a dose-response meta-analysis in 2017 combining data from 29 prospective cohort studies demonstrated neutral associations between dairy products and cardiovascular mortality16.

Potential dairy matrix mechanisms

The explanation for the finding that dairy foods, even those containing fat and saturated fat such as cheese, have a neutral or even a beneficial effect on CVD is likely to lie in the complex composition of the dairy matrix23.

Although some dairy foods contain saturated fatty acids, they are also rich in nutrients and bioactive components such as calcium, potassium, phosphorus and bioactive peptides that may modify CVD risk through, for example, positive effects on blood pressure, weight and diabetes. In addition, dairy constituents such as bioactive peptides may have direct effects on cardiovascular parameters including blood clotting, arterial stiffness endothelial function and inflammation24. This may help counter any negative effects of saturated fat in dairy on blood lipids and CVD risk. However, it is also increasingly recognised that individual saturated fatty acids have different effects on blood lipids; several of those in milk fat do not have an adverse effect on LDL (‘bad’) cholesterol or other markers of CVD risk including HDL (‘good’) cholesterol and the ratio of total to HDL cholesterol25. Moreover, components of the dairy matrix have been shown to modify blood lipid levels23.

There is evidence that calcium in dairy foods, through its effects on binding fat and decreasing its absorption in the gut, may reduce the potential rise in LDL cholesterol following saturated fat consumption26-28. For example, cheese does not increase LDL cholesterol compared with butter of equal fat content27. Similarly, compared with a low-calcium control diet, milk- and cheese-based diets lessened saturated fatty acid-induced increases in total and LDL cholesterol29. It may be important for this beneficial effect that fat and calcium are embedded in the same food matrix, as is the case for milk and cheese23. Phosphorus in the dairy matrix may also interact with calcium to influence blood lipids; calcium phosphate binds bile acids and fatty acids, and increases their excretion30. It has been suggested too that the membrane which encloses milk fat (the milk fat globule membrane; MFGM) and which is rich in bioactive phospholipids and proteins may have a beneficial role in modulating blood lipids31. Fermented dairy foods may also modify blood lipids through favouring gut bacteria which produce short-chain fatty acids (SCFA), and which in turn have a positive effect on lipids32.

In addition, the total fatty acid profile of a food, not just its saturated fatty acid content, is important. Milk fat includes a number of fatty acids which may have beneficial effects on CVD risk factors such as blood lipids and markers of inflammation. These include conjugated linoleic acid (cis-9, trans-11 CLA) and trans palmitoleic acid (trans-C16:1)33-35. A recent study reported that higher levels of a biomarker of dairy fat in the diet were associated with a lower incidence of CVD and CVD risk factors36.

It is evident that in terms of the effects of milk and dairy foods on cardiovascular health, the whole food, and the dietary pattern, rather than an individual component such as saturated fat should be taken into account. In this respect, the weight of epidemiological evidence suggests no adverse effects of regularly consuming milk and dairy foods on cardiovascular health and rather, in some studies, a cardio-protective effect has been observed.

References

1. Elwood PC et al. Milk drinking, ischaemic heart disease and ischaemic stroke II. Evidence from cohort studies. Eur J Clin Nutr. 2004; 58: 718-724.

2. Goldbohm RA et al. Dairy consumption 10-y total and cardiovascular mortality: a prospective cohort study in the Netherlands. Am J Clin Nutr. 2011; 93: 615-627.

3. van Aerde MA et al. Dairy intake in relation to cardiovascular disease mortality and all-cause mortality: the Hoorn Study. Eur J Nutr. 2013; 52: 609-616.

4. Praagman J et al. Dairy products and the risk of stroke and coronary heart disease the Rotterdam Study. Eur J Nutr. 2015; 54: 981-990.

5. Dalmeijer GW et al. Dairy intake and coronary heart disease or stroke-a population-based cohort study. Int J Cardiol. 2013; 167: 925-929.

6. Larsson SC et al. Dairy consumption and risk of stroke in Swedish women and men. Stroke. 2012; 43: 1775-1780.

7. Sonestedt E et al. Dairy products and its association with incidence of cardiovascular disease: the Malmö diet and cancer cohort. Eur J Epidemiol. 2011; 26: 609-618.

8. Michaëlsson K et al. Milk intake and risk of mortality and fractures in women and men: cohort studies. BMJ. 2014; 349: g6015.

9. Hellstrand S. The statistical analysis and reality. Letter to BMJ. BMJ. 2014; 349: g6015.

10. Bergholdt HK et al. Milk intake is not associated with low risk of diabetes or overweight-obesity: a Mendelian randomization study in 97,811 Danish individuals. Am J Clin Nutr. 2015; 102: 487-496.

11. Bongard V et al. Association of dietary patterns with 14-year all-cause mortality and cause-specific mortality. Eur Heart J.  2012; 33 (S1): 609-610.

12. 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: 659-669.

13. Elwood PC et al. The consumption of milk and dairy foods and the incidence of vascular disease and diabetes: an overview of the evidence. Lipids. 2010; 45: 925-939.

14. Soedamah-Muthu SS et al. Milk and dairy consumption and incidence of cardiovascular diseases and all-cause mortality: dose-response meta-analysis of prospective cohort studies. Am J Clin Nutr. 2011; 93: 158-171.

15. Larson SC et al. Milk consumption and mortality from all causes, cardiovascular disease, and cancer: a systematic review and meta-analysis. Nutrients. 2015; 7: 7749-7763.

16. Guo J et al. Milk and dairy consumption and risk of cardiovascular diseases and all-cause mortality: dose-response meta-analysis of prospective cohort studies. Eur J Epidemiol. 2017 Apr; 32(4): 269-287. doi: 10.1007/s10654-017-0243-1.

17. Drouin-Chartier J-P et al. Systematic review of the association between dairy product consumption and risk of cardiovascular-related clinical outcomes. Adv Nutr. 2016; 7: 1026–1040.

18. Qin LQ et al. Dairy consumption and risk of cardiovascular disease: an updated meta-analysis of prospective cohort studies. Asia Pac J Clin Nutr. 2015; 24: 90-100.

19. Hu D et al. Dairy foods and risk of stroke: a meta-analysis of prospective cohort studies. Nutr Metab Cardiovasc Dis. 2014; 24: 460-469.

20. de Goede J et al. Dairy consumption and risk of stroke: a systematic review and updated dose-response meta-analysis of prospective cohort studies. J Am Heart Assoc. 2016 May 20; 5(5). doi: 10.1161/JAHA.115.002787.

21. Alexander D et al. Dairy consumption and CVD: a systematic review and meta-analysis. Br J Nutr. 2016; 115: 737–750.

22. Chen GC et al. Cheese consumption and risk of cardiovascular disease: a meta-analysis of prospective studies. Eur J Nutr. 2016 Aug 12; DOI: 10.1007/s00394-016-1292-z.

23. Thorning TK et al. Whole dairy matrix or single nutrients in assessment of health effects: current evidence and knowledge gaps. Am J Clin Nutr 2017: 105:1–13.

24. Ricci-Cabello et al. Possible role of milk-derived bioactive peptides in the treatment and prevention of metabolic syndrome. Nutr Rev. 2012; 70: 241-255.

25. Kris-Etherton PM & Yu S. Individual fatty acid effects on plasma lipids and lipoproteins: human studies. Am J Clin Nutr. 1997; 65: 1628S-1644S.

26. Lorenzen JK & Astrup A. Dairy calcium intake modifies responsiveness of fat metabolism and blood lipids to a high-fat diet. Br J Nutr. 2011; 105: 1823-1831.

27. Soerensen KV et al. Effect of dairy calcium from cheese and milk on fecal fat excretion, blood lipids, and appetite in young men. Am J Clin Nutr. 2014; 99: 984-991. Epub ahead of print 12 March 2014. DOI: 10.3945/ajcn.113.077735.
28. Lorenzen JK et al. Milk minerals modify the effect of fat intake on serum lipid profile: results from an animal and a human short-term study. Br J Nutr. 2014; 111: 1412-1420.

29. Hjerpsted J et al. Cheese intake in large amounts lowers LDL-cholesterol concentrations compared with butter intake of equal fat content. Am J Clin Nutr. 2011; 94: 1479-1484.

30. Govers MJ et al. Characterization of the adsorption of conjugated and unconjugated bile acids to insoluble, amorphous calcium phosphate. J Lipid Res. 1994; 35: 741–748.

31. Rosqvist F et al. Potential role of milk fat globule membrane in modulating plasma lipoproteins, gene expression, and cholesterol metabolism in humans: a randomized study. Am J Clin Nutr. 2015; 102: 20-30.

32. St-Onge MP et al. Consumption of fermented and nonfermented dairy products: effects on cholesterol concentrations and metabolism. Am J Clin Nutr. 2000; 71: 674–681.

33. Tricon S et al. Opposing effects of cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid on blood lipids in healthy humans. Am J Clin Nutr. 2004; 80: 614-620.

34. Mozaffarian D et al. Trans-palmitoleic acid, metabolic risk factors, and new-onset diabetes in US adults: a cohort study. Ann Intern Med. 2010; 153: 790-799.

35. Kratz et al. The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease. Eur J Nutr. 2013; 52: 1-24.

36. de Oliveira Otto MC et al. Biomarkers of dairy fatty acids and risk of cardiovascular disease in the multi-ethnic study of atherosclerosis. J Am Heart Assoc. 2013; 2: e000092.

 

 

This website uses cookies to improve user experience. By using our website you consent to all cookies in accordance with our Cookie Policy.