Longitudinal association of dairy consumption with the changes in blood pressure and the risk of incident hypertension: the Framingham Heart Study

Owing to the well-established risk associated with hypertension (HTN)( 1 ), the prevalence of HTN presents significant threats to public health in the USA( 2 ) and throughout the world( 3 ). The lifetime risk of developing HTN has been estimated to be almost 90 %( 4 ). The importance of lowering blood pressure (BP) for reducing stroke and myocardial infarction risk is also clearly demonstrated( 5 , 6 ). A 5 mmHg reduction in BP has been found to be associated with a 21 % lower risk of IHD and 34 % lower risk of stroke( 7 ). Dietary modification can be an effective strategy for HTN prevention( 8 ), and dairy products may be a critical component of that strategy( 9 ). The Dietary Approaches to Stop Hypertension Trial found that low-fat/fat-free dairy foods added significant benefits to vegetables and fruits in lowering BP( 9 ). Randomised clinical trials conducted to specifically examine whether dairy intake influences BP are inconclusive( 10 , 11 ). This is likely a result of their relative short study duration (mostly up to several weeks) and small sample size. On the other hand, recent reviews and meta-analyses of prospective cohort studies (with follow-up durations ranging from 2 to15 years)( 10 , 12 , 13 ) have suggested that milk (irrespective of fat content) and low-fat dairy products may facilitate the prevention of HTN. Although the meta-analyses also concluded that the findings for total high-fat dairy products or fermented dairy products are variable and overall no significant association was observed in relation to HTN incidence( 13 ), evidence is limited in quantity and quality. Additional evidence is warranted. Moreover, the possibility of different health effects of dairy fats as opposed to that in other animal foods (e.g. meat) remains largely unstudied and open to debate; very few studies have reported adverse health effects or associations with high-fat dairy consumption( 13 – 16 ). Greater dairy consumption may also correlate with healthier dietary patterns( 17 – 19 ), but not all existing studies of dairy consumption and BP or HTN have accounted for potential confounding by overall diet quality( 20 , 21 ). Finally, most of the existing longitudinal studies that examined the association between dairy intake and incident HTN only assessed dietary intake once at baseline. However, failing to account for the potential changes in dairy intake over long follow-up periods as well as changes in other health characteristics (such as weight) may weaken the relationship between dairy intake and HTN incidence. Therefore, the present study aimed to assess the consumption of various high-fat and low-fat dairy products in relation to the change in BP and the development of incident HTN accounting for overall diet quality. We used repeated measures of health, lifestyle and dietary factors (including dietary intake and overall diet quality) to assess changes in diet, health and lifestyle over an average 15-year follow-up.