Low-Fat Dairy Reduces Risk of Hypertension

Hypertension is often considered a silent disease as its lack of symptoms can allow it to remain unnoticed until a serious medical problem occurs such as a heart attack or stroke. Diet is deemed one of the strongest environmental influences on blood pressure, so prevention and treatment of hypertension frequently focuses on making informed food choices. A recent study by Talaei et al. reported a negative association between dairy consumption and hypertension independent of calcium intake, suggesting a number of the components of dairy products to offer antihypertensive effects [1]. After discussing their findings within wider research, it could be concluded that consuming 2-3 servings per day of low-fat dairy within a generally healthy diet may reduce risk of hypertension and the resulting health complications.

Hypertension (HT), or high blood pressure (BP), is suffered by 1 in 4 UK adults [2] and is diagnosed when BP measurements exceed 140/90mmHg [3]. Elevated BP is considered one of the major modifiable risk factors for cardiovascular disease (CVD) as high blood flow through blood vessels excessively stretches the endothelium, causing stiffening [4] and greater susceptibility to potentially fatal obstruction and haemorrhage, which can result in heart attack, chronic heart failure and ischaemic stroke [5].

Most cases of high BP are diagnosed as primary HT, where risk is affected by genetic and lifestyle factors [6]. Consequently, provision of nutritional advice is common practice in the management of HT [7], for example the DASH diet (Dietary Approaches to Stop Hypertension), endorsing high consumption of fruits and vegetables and whole grains, low sodium intake, and replacement of trans and saturated fats (SFA) with unsaturated fats [8], has demonstrated to significantly reduce both systolic and diastolic BP [9].

The DASH diet also recommends daily consumption of 2-3 servings of dairy due to its proposed anti-hypertensive effects. Dairy products such as milk, yoghurt and cheese are rich sources of protein, minerals such as calcium, potassium, magnesium and phosphorous, and vitamin D [10], which may all act individually or in combination to lower BP. However, a causal relationship with any particular component(s) has not yet been found. A recent study by Talaei et al. analysed the association between HT and both dairy and calcium intake. Studying a population with high calcium intake from non-dairy sources allowed them to determine whether any observed relationship was as a consequence of the calcium content alone or other nutrients present [1]. This review will discuss their findings in the context of wider literature to determine whether high dairy intake should be recommended as a method of reducing risk of HT, or whether similar effects could be achieved with high dietary calcium intake.

Method

Study population

Data used was from the Singapore Chinese Health Study of Chinese women and men aged 45-74 years. Demographic characteristics, lifestyle and dietary information and medical history were obtained at recruitment and at two follow-up interviews.

Dietary and hypertension assessment

Dairy intake was assessed by a validated 165 item FFQ.

Diagnosed past medical conditions were reported by participants, and they were asked whether they suffered from HT at recruitment and both follow-up interviews.

Statistical analysis

The association between risk of HT and quartiles of total dairy intake, milk intake and calcium intake at baseline were estimated by Cox proportional hazard regression, with adjustment for lifestyle and dietary factors. A sensitivity analysis was performed using two dietary patterns to replace the food items.

Results

Subject characteristics

A total of 37,134 individuals were studied for an average of 9.5 years. 13,148 cases of hypertension were reported. Median dairy intake was 28.2g/day, with milk comprising 80% of the products consumed. Dairy consumers were more likely to do more physical activity, and less likely to smoked and consume alcohol. Median total calcium intake was 373mg/day with dairy calcium contributing 18.8% and non-dairy 80.2% of total calcium intake.

Results of statistical analysis

There was an inverse association between high dairy intake at baseline and risk of HT, which remained significant after adjustment. A 6% decreased risk of HT was found for those who drank milk daily. Adjustment for dietary pattern did not change the association.

Those in the highest quartile of total calcium intake had the lowest risk of HT. There was a similar association for dairy calcium but no association between non-dairy calcium and risk of hypertension.

Discussion

The study by Talaei et al. observed an inverse association between dairy intake and risk of hypertension [1], a result common within wider research. Soedamah-Muthu et al. found each 200g/day increment of dairy intake to offer a 3% reduced risk of HT [10], and Ralston et al. reported a 13% reduced risk of elevated BP from a total of 3-4 servings per day compared to the lowest category of intake [11]. Moreover, Drouin-Chartier et al. reported an improvement in endothelial function in subjects with dairy intake of 3.4 servings/day [12] suggesting a potential reduction in risk of HT and CVD. Despite these findings, Engberink et al. saw no association between total dairy and risk of HT after 5 years [13] and, in a further study, that an association observed after 2 years of follow up was attenuated after 6 years [14]. This suggests that dairy intake may only be a short-term predictor of HT risk, with it slowing progression but not preventing development [13]. However, data collected over a prolonged time period may hold inaccuracies as a consequence of participant misclassification where dietary changes have been made during the study in response to diagnosed health problems. It is therefore of importance that Talaei et al. obtained data on habitual diet at baseline and during both follow up interviews so changes could be recorded and subjects grouped appropriately.

When offering dietary advice, it should be of importance to consider type of dairy to recommend in addition to the quantity. An inverse association has been reported between low-fat dairy and HT [10], with a 10-15% reduced risk for those in the highest compared to the lowest quintile [15]. However, high-fat dairy often shows no association as SFA is thought to mitigate any benefits. The inverse relationship between dairy and HT has been shown to strengthen in individuals consuming <11.2% daily energy from SFA [16], which may result from the reduction in calcium absorption and bioavailability when it is combined with fats [15]. This suggests that milk products may offer more significant antihypertensive effects [10] than cheeses [13], which contains three times as much SFA as low fat milk [11]. Additionally, while fermented products such as yoghurt have a high peptide content [17], indicating the potential for inhibition of angiotensin-converting enzyme activity and modulation of endothelium function [13], like high-fat dairy, it has been observed that there is no association with HT risk [10].

Talaei et al. found an inverse association between calcium and HT [1], as is similar to other studies [15][18]. This is generally thought to be a consequence of the responsiveness of intracellular calcium concentration to dietary manipulation [19] as low calcium intake stimulates secretion of parathyroid hormone and the active form of vitamin D, increasing influx into smooth muscle cells [20]. High intracellular calcium concentration augments vascular smooth muscle tone and increases vascular resistance, causing vasoconstriction and elevated BP [20], with an enhanced response to the renin-angiotensin system amplifying this further [21].

Although no association has been observed between HT and vitamin D [18], Wang et al. reported a stronger inverse association between calcium and HT with lower vitamin D intake [15] which may be due to its role in promoting calcium uptake by cells, the importance of which has been previously described. However, vitamin D increases intestinal calcium absorption [15], and so its bioavailability, and it has been hypothesised that deficiency in vitamin D may activate the renin-angiotensin system causing vasoconstriction [22]. Despite these theories, the lack of studies investigating the role of vitamin D in BP regulation means it cannot be concluded whether fortification of dairy products may enhance or lessen their antihypertensive effect.

Finally, the association between calcium and HT being observed by Talaei et al. in dairy but not non-dairy calcium [1], suggests that other minerals present in dairy products are likely to have antihypertensive effects, for example magnesium and potassium. Magnesium is a cofactor in prostaglandin E synthesis, causing vasodilation [23], modifies production and release of nitric oxide [24], which affects endothelial function and arterial stiffness [25], and high extracellular magnesium concentration inhibits calcium influx by the blocking of calcium channels [24]. Moreover, dairy consumption increases plasma potassium concentration to stimulate the Na⁺/K⁺-ATPase pump, resulting in endothelium-dependent vasodilation [26]. These mechanisms indicate that the magnitude of the effect of dairy consumption on risk of HT is likely to rely on several micronutrients working in combination.

Impacts

To conclude, discussion of wider research has proven the validity of the inverse association observed by Talaei et al. between dairy intake and HT [1] due to the similarities within numerous other studies. However, it would not be possible to determine the magnitude of the effect due to the heterogeneity in classification on HT. Additionally, the biological plausibility of the antihypertensive effects of the various components of dairy products also reinforce the finding that they do not purely result from calcium component. 

Many of the studies consider high dairy consumption to be 3-4 servings/day, showing this to offer the greatest risk reduction. The recommendations in the DASH diet of intake of 2-3 servings of dairy every day, equating to approximately three 200ml glasses of milk, may be considered more practical advice for the general population, still being likely to provide observable benefits.  Nonetheless, it would be important that this is primarily low-fat dairy sources, such as semi-skimmed milk, due to the potentially mitigating effects of the high SFA content of products like cheese. The specific advice should also be complemented by a generally healthier lifestyle, particularly with a low sodium intake, to ensure a favourable sodium-potassium ratio is obtained [27]. This would prevent the benefits obtained by increased dairy consumption being attenuated so that an individual's risk of HT and CVD may be reduced.

---

[1] Talaei, M., Pan, A., Yuan, J-M., Koh, W-P. (2017) Dairy food intake is inversely associated with risk of hypertension: The Singapore Chinese health study. The Journal of Nutrition, jn238485.

[2] Public Health England (2014) New figures show high blood pressure costs NHS billions each year. Available at: https://www.gov.uk/government/news/new-figures-show-high-blood-pressure-costs-nhs-billions-each-year [2nd December 2016]

[3] NICE (2011) Hypertension in adults: Diagnosis and management. URL: https://www.nice.org.uk/guidance/cg127/chapter/1-Guidance#measuring-blood-pressure [1^st July 2017]

[4] Franklin, S.S. (2005) Arterial stiffness and hypertension: A two way street? Hypertension, 45, 345-351.

[5] Mensah, G.A., Brown, D.W. (2007) An overview of cardiovascular disease burden in the United States. Health Affairs, 26(1), 38-48.

[6] BUPA (2017?) High blood pressure (hypertension). URL: https://www.bupa.co.uk/health-information/directory/h/hypertension [1st July 2017]

[7] Guallar-Castillon, P., Munoz-Pareja, M., Aguilera, T., Leon-Munoz, L.M., Rodriguez-Artalejo, F. (2013) Food sources of sodium, saturated fat and added sugar in the Spanish hypertensive and diabetic population. Atherosclerosis, 229, 198-205.

[8] Chia, S., Bergeron, N., Williams, P.T., Bray, G.A., Sutherland, B., Krauss, R.M. (2016) Comparison of the DASH (Dietary Approaches to Stop Hypertension) diet and a higher-fat DASH diet on blood pressure and lipids and lipoproteins: A randomised controlled trial. The American Journal of Clinical Nutrition, 103, 341-7.

[9] Saneei, P., Salehi-Abargouei, A., Esmaillzadeh, A., Azadbakht, L. (2014) Influence of dietary approaches to stop hypertension (DASH) diet on blood pressure: A systematic review and meta-analysis on randomized controlled trials. Nutrition, Metabolism, and Cardiovascular Diseases, 24(12), 1253-1261.

[10] Soedamah-Muthu, S.S., Verberne, L.D.M., Ding, E.L., Engberink, M.F., Geleijnse, J.M. (2012) Dairy consumption and incidence of hypertension: A dose-response meta-analysis of prospective cohort studies. Hypertension, 60(5), 1131-1137.

[11] Ralston, R.A., Lee, J.H., Truby, H., Palermo, C.E., Walker, K.Z. (2012) A systematic review and meta-analysis of elevated blood pressure and consumption of dairy foods. Journal of Human Hypertension, 26, 3-13.

[12] Drouin-Chartier, J-P., Gigleux, I., Tremblay, A.J., Poirer, L., Lamarche, B., Couture, P. (2014) Impact of dairy consumption on essential hypertension: A clinical study. Nutrition Journal, 13(83).

[13] Engberink, M.F., Geleijnse, J.M., de Jong, N., Smit, H.A., Kok, F.J., Monique Verschuren, W.M. (2009) Dairy intake, blood pressure, and incident hypertension in a general dutch population. The Journal of Nutrition, 139(3), 582-587.

[14] Engberink, M.F., Hendriksen, M.A.H., Schouten, E.G., van Rooij, F.J.A., Hofman, A., Witterman, J.C.M., Geleijnse, J.M. (2009) Inverse association between dairy intake and hypertension: The Rotterdam study. The American Journal for Clinical Nutrition, 89, 1-7.

[15] Wang, L., Manson, J.E., Buring, J.E., Lee, I-M., Sesso, H.D. (2008) Dietary intake of dairy products, calcium, and vitamin D and the risk of hypertension in middle-aged and older women. Hypertension, 51(4), 1073-1079.

[16] Djoussé, L., Pankow, J.S., Hunt, S.C., Heiss, G., Province, M.A., Kabagambe, E.K., Ellison, R.C. (2006) Influence of saturated fat and linolenic acid on the association between intake of dairy products and blood pressure. Hypertension, 48(2), 335-341.

[17] Heraclides, A., Mishra, G.D., Hardy, R.J., Geleijnse, J.M., Black, S., Prynne, C.J., Kuh, D., Soedamah-Muthu, S.S. (2012) Dairy intake, blood pressure and incident hypertension in a general British population: The 1946 birth cohort. European Journal of Nutrition, 51, 583-591.

[18] Jorde, R., Bonaa, K.H. (2000) Calcium from dairy products, vitamin D intake, and blood pressure: The Tromso study. The American Journal of Clinical Nutrition, 71, 1530-1535.

[19] Hilpert, K.F., West, S.G., Bagshaw, D.M., Fishell, V., Barnhart, L., Lefevre, M., Most, M.M., Zemel, Chow, M., Hinderliter, A.L., Kris-Etherton, P.M. (2009) Effects of dairy products on intracellular calcium and blood pressure in adults with essential hypertension. Journal of the American College of Nutrition, 28(2), 142-149.

[20] Simonetti, G., Mohaupt, M. (2007) Calcium and blood pressure. Therapeutische Umschau, 64(5), 249-252.

[21] Pescatello, L.S., Turner, D., Rodriguez, N., Blanchard, B.E., Tsongalis, G.J., Maresh, C.M., Duffy, V., Thompson, P.D. (2007) Dietary calcium intake and renin angiotensin system polymorphisms alter the blood pressure reseponse to aerobic exercise: A randomized control design. Nutrition & Metabolism, 4(1).

[22] Zhou, C., Lu, F., Cao, K., Xu, D., Goltzman, D., Miao, D. (2008) Calcium-independent and 1,25(OH)₂D₃-dependent regulation of the renin-angiotensin system in 1α-hydroxylase knockout mice. Kidney International, 74(2), 170-179.

[23] Houston, M. (2011) The role of magnesium in hypertension and cardiovascular disease. The Journal of Clinical Hypertension, 13(11), 843-847.

[24] Rosa Cunha, A., Umbelino, B., Correia, M.L., Fritsch Neves, M. (2012) Magnesium and vascular changes in hypertension. International Journal of Hypertension, Article ID 754250.

[25] Hermann, M., Flammer, A., Lüscher, T.F (2006) Nitric oxide in hypertension. The Journal of Clinical Hypertension, 8(12 Supplement 4), 17-29.

[26] McGrane, M.M., Essery, E., Obbagy, J., Lyon, J., MacNeil, P., Spahn, J., Van Horn, L. (2011) Dairy consumption, blood pressure, and risk of hypertension: An evidence-based review of recent literature. Current Cardiovascular Risk Reports, 5(4), 287-298.

[27] Hedayati, S.S., Minhajuddin, A.T., Ijaz, A., Moe, O.W., Elsayed, E.F., Reilly, R.F., Huang, C-L. (2012) Association of urinary sodium/potassium ratio with blood pressure: Sex and racial differences. Clinical Journal of the American Society of Nephrology, 7(2), 315-322.