Coffee and High Blood Pressure

Summarized by Robert W. Griffith, MD
May 3, 2007

Summary

In a large Dutch 11-year cohort study, low-consumption coffee drinkers (1-3 cups a day) had a higher rate of hypertension than abstainers, and, in women, than those drinking 6 cups a day or more.

Introduction

Many studies have been done to try and determine whether coffee consumption causes high blood pressure, but the results have been inconsistent. Some studies show a positive relationship (i.e. coffee drinking is linked to high blood pressure), some show no relationship, and some show an inverse relationship (i.e. coffee lowers blood pressure). To help in reaching a definite conclusion, researchers in the Netherlands have conducted a long-term cohort study (this is where a group of subjects are studied from a baseline point for a number of years). The relationship of baseline coffee intake to the occurrence of persistent high blood pressure was studied, using repeatedly measured pressures at 5 year intervals over 11 years. The results are published in the American Journal of Clinical Nutrition, and summarized below.

What was done

A cohort of 2,985 men and 3,383 women was established in the Dutch city of Doetichem. Baseline enrollment was between 1987 and 1991. A first follow-up was done in 1993-1997, and a second in 1998-2002. The analysis included those who attended the baseline and at least one of the follow-up exams.

Coffee intake at baseline was determined by the question "how many cups of coffee do you drink a day?" followed by questions on the type of coffee taken and the use of additives (milk, sugar, etc). Participants also completed a food-frequency questionnaire, and provided information about tea intake as well as other health and demographic data. The subjects were classified into 4 categories according to their baseline coffee intake: 0 cups a day, 1-3 cups a day, 4-6 cups a day, and more than 6 cups a day.

At each exam body weight, height, fasting glucose levels and lipid levels were obtained. Sitting blood pressure was measured, then heart rate, followed by a second blood pressure measurement. Persistent hypertension was defined as an average systolic pressure of 140 mm Hg or above, or an average diastolic of 90 mm Hg or above, calculated over both follow-up measurements at a 5-year interval, or the use of antihypertensive medication at either of the follow-up exams.

What was found

The average age of participants at baseline was 40 years. Absence of high blood pressure (below 140/90 mm Hg and no antihypertensive medication) was found in 77% of the men and 86% of the women; these subjects were used for the further analyses of relationship to coffee intake.

Coffee abstainers (both sexes pooled) had a lower risk of persistent hypertension than did those who drank 1-3 cups of coffee a day. In fact, the odds ratio was 0.54, meaning that for every 100 low-coffee consumers who developed high blood pressure, there were only 54 abstainers who did so. With the sexes analyzed separately, the odds ratios were 0.6 for men, and 0.51 for women.

Here are the odds ratios for the different categories - the low-consumption coffee intake was set as 1.0:

	abstainers	1 - 3 cups	4 - 6 cups	over 6 cups
Men	0.60	1.0	1.08	1.03
Women	0.51	1.0	0.83	0.67*
Total	0.54*	1.0	0.93	0.83

* statistically significant difference from 1-3 cups/day

The only other statistically significant difference was in the women who drank over 6 cups daily. In women, a J-shaped curve phenomenon was clear - highest risk with 1-3 cups daily, lower risks for abstainers and those taking more than 3 cups daily. This effect was not seen in men.

What these findings mean

It must be made clear that the odds ratios reported above were obtained after allowances had been made for the factors known to affect the development of high blood pressure: age, sex, body height and weight, smoking, alcohol intake, tea intake, educational level, occupational status, and total calorie intake. This indicates that low-consumption coffee intake is an independent risk factor for high blood pressure - more so in women than in men.

A similar, but not identical, effect has been reported previously (see first link below). Women's caffeine intake in the Nurses Health Studies was analyzed and found to show a similar J-shaped blood pressure relationship to the coffee intake in this study. However, the full analysis showed that coffee was not guilty in the Nurses study, but rather cola drinks (both sugared and diet colas). Cola drinks are relatively uncommon in the Netherlands, and obviously didn't play a role in the Dutch study we've summarized.

What's to be done with the information from this study? Stated simply, it seems better to drink no coffee or a lot of coffee, just not 'moderate consumption'. This is different from our usual problem, which is solved by recommending 'moderation in all things' - think of alcohol intake. All that we can recommend is to drink coffee as much or as little as you like, but check your blood pressure regularly.

Source

• Coffee intake and incidence of hypertension. CSPM. Uiterwaal, WMM. Verschuren, HB. Bueno-de-Mesquita,  et al. , Am J Clin Nutr, 2007, vol. 85, pp. 718--723

Related Links
The Blood Pressure Villain is Cola, not Caffeine
Older Coffee Drinkers May Have the Edge
Is Coffee Good or Bad? - Another Piece of Evidence

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