Dairy intake, blood pressure and hypertension: observational and intervention studies.

Background Worldwide the prevalence of hypertension is increasing rapidly, which calls for effective public health measures. Whether dairy intake could play a role in reducing population blood pressure is not yet clear. The objective of this thesis was to examine the association of dairy intake with blood pressure level and incident hypertension in the Dutch population, and to assess the blood pressure effect of two ‘promising’ dairy components, i.e. lactotripeptides (ipp and vpp) and cis-9, trans-11 conjugated linoleic acid (cla). Methods Intakes of total dairy and types of dairy were examined in relation to blood pressure level in 21,553 Dutch adults aged 20-65 y from the morgen study. The risk of hypertension was examined in 3454 of these participants with 5 y of follow-up and in 2245 older Dutch adults from the Rotterdam study with 6 y of follow-up. The blood pressure effect of lactotripeptides was assessed in an 8-week, randomized controlled trial in 135 middle-aged Dutch subjects with elevated blood pressure. The effect of a high dose of cis-9, trans-11 cla on blood pressure was studied in a 9-week, randomized cross-over trial in 61 young, normotensive Dutch subjects. Results Blood pressure levels were not consistently related to overall dairy intake or intake of specific dairy foods in the general Dutch population (morgen study). Longitudinal analyses in the morgen study and the Rotterdam study showed a ~20% reduced risk of hypertension in subjects who consumed more than 150 mL (~1 serving) of low-fat dairy per day, whereas other dairy foods were not consistently associated with incident hypertension. Blood pressure was not affected by intervention with lactotripeptides. The mean difference (95% confidence interval) in systolic blood pressure response between the treatment and control group was 2.8 mm Hg (–2.6, 8.2) for lactotripeptides obtained by fermentation, –0.5 mm Hg (–6.0, 5.0) for lactotripeptides obtained by enzymatic hydrolysis, and 1.6 mm Hg (–3.9, 6.9) for synthetic lactotripeptides (p = 0.46). With regard to intervention with cis-9, trans-11 cla, systolic blood pressure changed –0.1 mm Hg (–1.49, 1.27) compared to control treatment (oleic acid), which was not statistically significant (p = 0.87). Conclusion The findings presented in this thesis suggest that low-fat dairy products may reduce the risk of hypertension. However, it should be noted that evidence has mainly been derived from observational studies and controlled intervention studies are needed to confirm these findings. With regard to dairy components, we conclude that lactotripeptides and cla are unlikely to play an important role in blood pressure regulation. Current dietary guidelines in countries like the us and the Netherlands include 2-3 servings of low-fat or fat-free dairy per day, which is mainly based on the prevention of osteoporosis by ensuring an adequate intake of calcium. Based on the findings presented in this thesis, and evidence from the scientific literature, there is at present no need to adapt these recommendations for the purpose of hypertension prevention.