Study: Coffee and high blood pressure

Relation

Chei CL, Loh JK, Soh A, Yuan JM, Koh WP. Coffee, tea, caffeine and risk of high blood pressure: The Singapore Chinese Health Study.Your J Nutr. March 1, 2017. doi: 10.1007/s00394-017-1412-4. [Epub ahead of print]

Draft

Population-based prospective cohort

Study objective

Determining the association between coffee and tea consumption and hypertension.

Participant

Data were collected from the Singapore Chinese Health Study, a population-based prospective cohort that recruited 63,257 Chinese participants aged 45 to 74 years living in Singapore from 1993 to 1998. Information on coffee and tea consumption and other lifestyle factors was collected at baseline. Self-reported physician-diagnosed hypertension was assessed in 2 follow-up interviews (1999-2004, 2006-2010).

Study medication and dosage

Recruitment used face-to-face interviews to collect information on demographics, height, weight, lifetime tobacco use, current physical activity, sleep duration, and medical history. A detailed questionnaire was used to collect information on food consumption, including alcohol, coffee and tea. These questionnaires included frequency of intake of standard servings of coffee, black tea, and green tea using 9 categories: never or almost never; 1 to 3 times a month; weekly; 2 to 3 times a week; 4 to 6 times per week; once a day; 2 to 3 times a day; 4 to 5 times a day; and 6 or more times a day.

Target parameters

Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of hypertension associated with coffee, black tea, green tea, and caffeine intake.

Key insights

Over an average follow-up of 9.5 years, 13,658 cases of hypertension were diagnosed in the cohort. The hypertensive patients were more likely to be women, never smokers and non-drinkers of alcohol. They were also older, less educated, had a higher body mass index (BMI) and were more physically active. The results of the multivariable analysis showed an inverse U-shaped association between coffee consumption and hypertension risk. Compared to drinking 1 cup per day, drinking coffee less often was associated with a lower risk of high blood pressure. Similarly, the risk was also reduced in those who drank more than 2 cups per day. In multivariable analysis, compared to those who drank 1 cup per day, incident hypertension heart rates were as follows: 0.94 (95% CI: 0.88-1.00) for weekly to

Consider how this might translate into clinical practice: If you're talking to a patient with mild hypertension who admits to drinking 1 cup of coffee every morning, your advice, based on this study, should be, "Either stop drinking coffee or start drinking a lot more."

The association between coffee consumption and the occurrence of hypertension did not differ significantly between men and women (P<0.5 for all interactions). See illustration.

figure

Participants who drank black tea daily had a slightly increased risk (9%) compared to those who drank black tea less than weekly (HR: 1.09; 95% CI: 1.03-1.15). Similar results were observed for green tea (HR: 1.06; 95% CI: 1.00-1.11). However, these associations were not statistically significant when adjusted for caffeine content.

There was a statistically significant positive association between caffeine intake and the risk of hypertension; Compared with caffeine intake <50 mg/day, all 4 higher categories of caffeine intake had a statistically significant increase in the risk of hypertension, but without a clear dose-dependent trend.

After adjusting for coffee (so that caffeine intake came from other sources), the gradual dose-response relationship between caffeine intake and hypertension risk became clearer. Compared to the lowest intake (<50 mg/day), the multivariable HRs for 50 to <100, 100 to <200, 200 to <300, ≥300 mg per day were 1.07 (95% CI: 1.00-1.15), 1.10 (95% CI: 1.02-1.18), 1.08 (95 % CI: 0.98–1.19) and 1.16 (95% CI: 1.04-1.31;Pfor trend=0.02).

Practice implications

Participants who drank less than 1 cup of coffee per week or more than 2 cups of coffee per day had a significantly lower risk of high blood pressure compared to those who drank 1 cup per day.

Consider how this translates to clinical practice: If you're talking to a patient with mild hypertension who admits to drinking 1 cup of coffee every morning, your advice based on this study should be, "Either stop drinking coffee or start drinking a lot more."

As strange as it sounds, we should take these results seriously. They are consistent with conclusions from a 2011 dose-response meta-analysis of 5 cohort studies, which also suggested an inverted U-shaped or J-shaped association between coffee and the risk of high blood pressure.¹In this meta-analysis, the risk of hypertension increased with coffee consumption, peaking at 3 cups per day, but the risk decreased with higher coffee consumption. These current Chei findings are also similar to several prospective studies that have found a nonlinear association between cohorts of European men and women.^2.3US nurses,⁴and other health professionals.⁵Moderate coffee drinkers (1-3 cups/day) were found to have the highest risk of high blood pressure compared to light drinkers who drank less than 1 cup per day and heavy drinkers who drank more than 3 cups per day. A 2007 Dutch study reported a similar inverse J-shaped association, in which the risk of hypertension was reduced for those who drank less than 1 cup of coffee per day and for those who drank more than 3 cups per day, compared to those who drank 1 to 3 cups per day.⁶These current findings further confirm what at first glance appears to be a strange phenomenon, the inverted U-shaped dose-response curve.

Not surprisingly, caffeine increases blood pressure; This occurs through “mechanisms that include sympathetic overactivation, antagonism of adenosine receptors, an increase in norepinephrine release through direct effects on the adrenal medulla, direct renal effects, and activation of the renin-angiotensin system.”⁷However, coffee appears to have other properties, so high doses blunt the effects of caffeine.

Coffee is a rich source of potassium and 5 cups per day provides about 26% of your daily potassium intake.⁸Potassium promotes vascular smooth muscle relaxation and endothelium-dependent vasodilation, increases endothelial nitric oxide production, and has antihypertensive effects in animals and humans.⁹Chlorogenic acid, an important polyphenol in coffee, may also be responsible for coffee's blood pressure-lowering effects. Chlorogenic acid has been shown to reduce blood pressure and improve endothelial dysfunction in hypertensive rats¹⁰and in mildly hypertensive people.¹¹

So what's going on is that moderate doses of coffee in the range of 1 to 2 cups per day increase the risk of high blood pressure due to the influence of caffeine. At higher doses, these other chemicals can counteract the effects of caffeine and lower blood pressure.

If coffee's effect on blood pressure is indeed dose-specific, this could explain the inconsistencies found in other epidemiological studies looking for links between coffee consumption and cardiovascular disease.¹²

By the way, although technically a cup of coffee is usually defined as 150 ml of liquid, or about 5 fluid ounces, rather than the 8 ounces that normally make up a cup, in this recent study a cup of coffee was defined as 237 ml. an almost full 8-ounce cup.

U-shaped dose-response curves are more commonly reported in the literature and we must assume that this form of response is more common than originally thought. As a result, it is likely that our diet and nutrition recommendations will become more complex in the future as we recognize that effects may change with changes in dose size. While more isn't always better, in the case of coffee it just may be.