Dairy products and cardiovascular disease

Dairy consumption and patterns of mortality of Australian adults

BACKGROUND/OBJECTIVES

Dairy foods contain various nutrients that may affect health. We investigated whether intake of dairy products or related nutrients is associated with mortality due to cardiovascular disease (CVD), cancer and all causes.

SUBJECTS/METHODS

We carried out a 16-year prospective study among a community-based sample of 1529 adult Australians aged 25-78 years at baseline. Habitual intakes of dairy products (total, high/low-fat dairy, milk, yoghurt and full-fat cheese), calcium and vitamin D were estimated as mean reported intake using validated food frequency questionnaires (FFQs) self-administered in 1992, 1994 and 1996. National Death Index data were used to ascertain mortality and cause of death between 1992 and 2007. Hazard ratios (HRs) were calculated using Cox regression analysis.

RESULTS

During an average follow-up time of 14.4 years, 177 participants died, including 61 deaths due to CVD and 58 deaths due to cancer. There was no consistent and significant association between total dairy intake and total or cause-specific mortality. However, compared with those with the lowest intake of full-fat dairy, participants with the highest intake (median intake 339 g/day) had reduced death due to CVD (HR: 0.31; 95% confidence interval (CI): 0.12-0.79; P for trend=0.04) after adjustment for calcium intake and other confounders. Intakes of low-fat dairy, specific dairy foods, calcium and vitamin D showed no consistent associations.

CONCLUSIONS

Overall intake of dairy products was not associated with mortality. A possible beneficial association between intake of full-fat dairy and cardiovascular mortality needs further assessment and confirmation.

The effect of dairy foods on CHD: a systematic review of prospective cohort studies

There is interest in the degree to which fats in dairy foods contribute to CHD. We undertook a systematic review to investigate the effect of dairy consumption on CHD using prospective cohort studies. A systematic search of electronic databases identified studies relating dairy food intake in adulthood to episodes or death from CHD, IHD and myocardial infarction. Included studies were assessed for quality based on study methodology, validity of dietary assessment, success of follow-up, standardised assessment of CHD, IHD or myocardial infarction end points and appropriateness of statistical adjustment. Data from twelve cohorts involving >280,000 subjects were included. Most studies had follow-up of >80 %, adjusted statistically for three or more confounders and used standard criteria to determine end points. About half the studies used a validated FFQ, administered the FFQ more than once or had follow-up of >20 years. Fewer than half the studies involved subjects representative of the general population. Four of the twelve cohorts found no association between dairy intake and CHD. Eight studies reported varying relationships between different dairy foods and CHD or differential associations based on race, sex or over time. Although dairy foods contribute to the SFA composition of the diet, this systematic review could find no consistent evidence that dairy food consumption is associated with a higher risk of CHD. This could be due to the limited sensitivity of the dietary assessment methods to detect an effect of a single food in a mixed diet on complex clinical outcomes.

Stroke and plasma markers of milk fat intake--a prospective nested case-control study

Background

Dairy products are high in saturated fat and are traditionally a risk factor for vascular diseases. The fatty acids 15:0 and 17:0 of plasma lipids are biomarkers of milk fat intake. The aim of the present study was to evaluate the risk of a first-ever stroke in relation to the plasma milk fat biomarkers.

Methods

A prospective case-control study was nested within two population based health surveys in Northern Sweden. Among 129 stroke cases and 257 matched controls, plasma samples for fatty acid analyses were available in 108 cases and 216 control subjects. Proportions of 15:0 and 17:0 of plasma lipids, weight, height, blood lipids, blood pressures, and lifestyle data were employed in conditional logistic regression modelling.

Results

The proportions of fatty acids 17:0 and 15:0+17:0 of total plasma phospholipids were significantly higher in female controls than cases, but not in men. 17:0 and 15:0+17:0 were significantly and inversely related to stroke in the whole study sample as well as in women. The standardised odds ratio (95% CI) in women to have a stroke was 0.41 (0.24–0.69) for 17:0 in plasma phospholipids. Adjustment for traditional cardiovascular risk factors, physical activity and diet had marginal effects on the odds ratios. A similar, but non-significant, trend was seen in men.

Conclusion

It is hypothesised that dairy or milk fat intake may be inversely related to the risk of a first event of stroke. The intriguing results of this study should be interpreted with caution. Follow up studies with greater power, and where intakes are monitored both by dietary recordings and fatty acid markers are needed.

A reappraisal of the impact of dairy foods and milk fat on cardiovascular disease risk

Background

This review provides a reappraisal of the potential effects of dairy foods, including dairy fats, on cardiovascular disease (CVD)/coronary heart disease (CHD) risk. Commodities and foods containing saturated fats are of particular focus as current public dietary recommendations are directed toward reducing the intake of saturated fats as a means to improve the overall health of the population. A conference of scientists from different perspectives of dietary fat and health was convened in order to consider the scientific basis for these recommendations.

Aims

This review and summary of the conference focus on four key areas related to the biology of dairy foods and fats and their potential impact on human health: (a) the effect of dairy foods on CVD in prospective cohort studies; (b) the impact of dairy fat on plasma lipid risk factors for CVD; (c) the effects of dairy fat on non-lipid risk factors for CVD; and (d) the role of dairy products as essential contributors of micronutrients in reference food patterns for the elderly.

Conclusions

Despite the contribution of dairy products to the saturated fatty acid composition of the diet, and given the diversity of dairy foods of widely differing composition, there is no clear evidence that dairy food consumption is consistently associated with a higher risk of CVD. Thus, recommendations to reduce dairy food consumption irrespective of the nature of the dairy product should be made with caution.

1H NMR metabonomics can differentiate the early atherogenic effect of dairy products in hyperlipidemic hamsters

Diet is an important environmental factor modulating the onset of atherosclerosis. The aim of this study was to evaluate the effects of different dairy-based food products on early atherogenesis using both conventional and metabonomic approaches in hyperlipidemic hamsters. The hamsters received up to 200 g/kg of fat as anhydrous butter or cheese made from various milk fats or canola-based oil (CV), in addition to a non-atherogenic low-fat diet. Aortic cholesteryl ester loading was considered to be an early atherogenic point, and metabolic changes linked to atherogenesis were measured using plasma (1)H NMR-based metabonomics. The lowest atherogenicity was obtained with the plant-oil cheese diet, followed by the dairy fat cheese diet, while the greatest atherogenicity was observed with the butter diet (P<0.05). Disease outcome was correlated with conventional plasma biomarkers (total cholesterol, triglycerides, LDL cholesterol, R(2)=0.42-0.60). NMR plasma metabonomics selectively captured part of the diet-induced metabotypes correlated with aortic cholesteryl esters (R(2)=0.63). In these metabotypes, VLDL lipids, cholesterol, and N-acetylglycoproteins (R(2) range: 0.45-0.51) were the most positively correlated metabolites, whereas a multimetabolite response at 3.75 ppm, albumin lysyl residues, and trimethylamine-N-oxide were the most negatively correlated metabolites (R(2) range: 0.43-0.63) of the aortic cholesteryl esters. Collectively, these metabolites predicted 89% of atherogenic variability compared to the 60% predicted by total plasma cholesterol alone. In conclusion, we show that the food environment can modulate the atherogenic effect of dairy fat. This proof-of-principle study demonstrates the first use of plasma metabonomics for improving the prognosis of diet-induced atherogenesis, revealing novel potential disease biomarkers.

A diet rich in conjugated linoleic acid and butter increases lipid peroxidation but does not affect atherosclerotic, inflammatory, or diabetic risk markers in healthy young men

Intake of conjugated linoleic acid (CLA) has been demonstrated to beneficially affect risk markers of atherosclerosis and diabetes in rats. CLA is naturally found in milk fat, especially from cows fed a diet high in oleic acid, and increased CLA intake can occur concomitantly with increased milk fat intake. Our objective was to investigate the effect of CLA as part of a diet rich in butter as a source of milk fat on risk markers of atherosclerosis, inflammation, diabetes type II, and lipid peroxidation. A total of 38 healthy young men were given a diet with 115 g/d of CLA-rich fat (5.5 g/d CLA oil, a mixture of 39.4% cis9, trans11 and 38.5% trans10, cis12) or of control fat with a low content of CLA in a 5-wk double-blind, randomized, parallel intervention study. We collected blood and urine before and after the intervention. The fatty acid composition of plasma triacylglycerol, cholesterol esters, and phospholipids reflected that of the intervention diets. The CLA diet resulted in increased lipid peroxidation measured as an 83% higher 8-iso-prostaglandin F2alpha concentration compared with the control, P < 0.0001. We observed no other significant differences in the effect of the interventions diets. In conclusion, when given as part of a diet rich in butter, a mixture of CLA isomers increased lipid peroxidation but did not affect risk markers of cardiovascular disease, inflammation, or fasting insulin and glucose concentrations.

Plasma and erythrocyte biomarkers of dairy fat intake and risk of ischemic heart disease

BACKGROUND

The relation between dairy product intake and the risk of ischemic heart disease (IHD) remains controversial.

OBJECTIVE

We aimed to explore biomarkers of dairy fat intake in plasma and erythrocytes and to assess the hypothesis that higher concentrations of these biomarkers are associated with a greater risk of IHD in US women.

DESIGN

Among 32,826 participants in the Nurses' Health Study who provided blood samples in 1989-1990, 166 incident cases of IHD were ascertained between baseline and 1996. These cases were matched with 327 controls for age, smoking, fasting status, and date of blood drawing.

RESULTS

Among controls, correlation coefficients between average dairy fat intake in 1986-1990 and 15:0 and trans 16:1n-7 content were 0.36 and 0.30 for plasma and 0.30 and 0.32 for erythrocytes, respectively. In multivariate analyses, with control for age, smoking, and other risk factors of IHD, women with higher plasma concentrations of 15:0 had a significantly higher risk of IHD. The multivariate-adjusted relative risks (95% CI) from the lowest to highest tertile of 15:0 concentrations in plasma were 1.0 (reference), 2.18 (1.20, 3.98), and 2.36 (1.16, 4.78) (P for trend = 0.03). Associations for other biomarkers were not significant.

CONCLUSIONS

Plasma and erythrocyte contents of 15:0 and trans 16:1n-7 can be used as biomarkers of dairy fat intake. These data suggest that a high intake of dairy fat is associated with a greater risk of IHD.

On the supposed influence of milk homogenization on the risk of CVD, diabetes and allergy

Commercial milk is homogenized for the purpose of physical stability, thereby reducing fat droplet size and including caseins and some whey proteins at the droplet interface. This seems to result in a better digestibility than untreated milk. Various casein peptides and milk fat globule membrane (MFGM) proteins are reported to present either harmful (e.g. atherogenic) or beneficial bioactivity (e.g. hypotensive, anticarcinogenic and others). Homogenization might enhance either of these effects, but this remains controversial. The effect of homogenization has not been studied regarding the link between early cow's milk consumption and occurrence of type I diabetes in children prone to the disease and no link appears in the general population. Homogenization does not influence milk allergy and intolerance in allergic children and lactose-intolerant or milk-hypersensitive adults. The impact of homogenization, as well as heating and other treatments such as cheesemaking processes, on the health properties of milk and dairy products remains to be fully elucidated.