Make Mine Espresso!
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips serves on the speaker's bureau of Cephalon, Boehringer Ingelheim, Merck, ResMed, and GlaxoSmithKline, and is a consultant for Boehringer Ingelheim, Wyeth-Ayerst, and ResMed.
Synopsis: Cola consumption, but not caffeine per se, was associated with increased risk of developing hypertension over a 12-year period.
Source: Winkelmayer WC, et al. Habitual caffeine intake and the risk of hypertension in women. JAMA. 2005;294: 2330-2335.
This prospective report from harvard used Nurses' Health Studies (NHS). Winkelmayer and colleagues used these cohorts to investigate the risk of incident hypertension over a 12-year follow-up. In brief, NHS I began in 1976 with 121,700 women who were 30-35 years of age, and NHS II began in 1989 with 116,671 women who were 25-42 years of age. Both studies are ongoing; every two years, the 238,371 participants give blood and other samples for tests and complete a lengthy questionnaire. Follow-up of these health professionals is a robust 90%.
The study sample for this analysis consisted of 162,728 women from both studies who did not have hypertension at baseline. Detailed dietary records enabled the investigators to calculate caffeine consumption using a validated approach, and beverage intake was subdivided into colas, diet colas, and regular and decaffeinated coffee and tea. Results controlled for age, body mass index, alcohol use, physical activity, smoking, family history, use of oral contraceptives, as well as intake of sodium, magnesium, calcium, potassium and phosphorus. Over an average follow-up of 12 years, 19,541 (12%) of these women developed physician-diagnosed hypertension. The relationship between caffeine intake and hypertension was an inverted U, with increased risk of developing hypertension for those in the lowest quintile (0-45 mg/day) and highest quintile (417-1788 mg/day). When the analyses were repeated using different caffeine-containing beverages, the authors found that neither caffeinated nor noncaffeinated coffee was associated with an increased risk of incident hypertension. In fact, there a marginally significant trend for a protective effect of caffeinated coffee on the risk of developing hypertension for both cohorts. The results for the relationship between decaffeinated coffee and hypertension were similar to those of caffeinated coffee and hypertension. However, there was a trend for increased risk of development of hypertension with caffeinated tea in the NHSII (younger) cohort.
The strongest finding of the study was an association between consumption of caffeinated cola, either diet or sugared, and the risk of development of hypertension. There was a linear, statistically significant relationship between numbers of glasses or cans of cola per day and the risk of incident hypertension. Adjustment for other risk factors did not change this finding.
Incidentally, Winkelmayer et al found a linear relationship between caffeine intake and both alcohol consumption and smoking in both cohorts, a finding which has previously been noted in other studies.1
Commentary
This study was widely quoted in the lay press. The lead author was quoted as saying, "There was a direct and positive association between cola consumption and the risk of high blood pressure. It was present in sugared cola and diet cola, and it was absolutely a surprise to us."2 In fact, based on the short-term effects of coffee on blood pressure,3 experimental work showing that caffeine raises levels of stress hormones including epinephrine and cortisol,4,5 and a small prospective study of caffeine intake in men,1 the results are surprising.
This report is the first prospective study of the effects of caffeine consumption on the long-term risk of hypertension in women. A prior longitudinal study of caffeine consumption in 1017 men in the Hopkins Precursor study demonstrated a positive association between drinking coffee and the unadjusted risk of developing hypertension,1 but the relationship was nonlinear (those drinking 5 or more cups of coffee appeared to be at lower risk than those drinking smaller amounts), and the differences were not statistically significant after adjustment for confounders. Further, the Hopkins study did not control for cola intake. The authors in that study concluded that coffee drinking "appears to play a small role in the development of hypertension." The current report includes a sample which was 100 times larger than that of the Hopkins study, and is probably closer to the truth. It suggests that women who drink 4 or more cups of coffee a day may actually be at reduced risk of developing hypertension.
The other noteworthy finding of this NHS is that cola of any sort was associated with increased incidence of hypertension (if Winkelmayer et al collected data on caffeine-free sodas, they do not report it here). They speculate, based partly on the results of the coffee analysis, that it is not the caffeine in cola that increases the risk of hypertension. They note that the glycemic load in colas may increase the risk of diabetes, but this notion raises more questions than it answers, since it doesn't explain the association between diet cola and hypertension. It is also possible that women who drink soda have some other characteristic that increases the risk of hypertension. Because of the precision and specificity of the dietary history and analyses in the NHS cohorts, this other characteristic is unlikely to be dietary.
This paper exonerating coffee as a cause of hypertension comes on the heels of a paper suggesting that coffee drinkers may have a reduced risk of developing diabetes.6 So those of us who have been telling our patients to avoid Starbucks may want to reconsider.
For now, coffee is cleared as a risk factor for hypertension, at least in women. Cola is bad. But we knew that.
References
1. Klag MJ, et al. Coffee intake and risk of hypertension: the Johns Hopkins precursors study. Arch Intern Med. 2002;162:657-662.
2. McKenna MAJ. High blood pressure, cola link possible. Cox News Service, November 09, 2005.
3. Jee SH, et al. The effect of chronic coffee drinking on blood pressure: a meta-analysis of controlled clinical trials. Hypertension. 1999;33:647-652.
4. Lane JD, et al. Caffeine effects on cardiovascular and neuroendocrine responses to acute psychosocial stress and their relationship to level of habitual caffeine consumption. Psychosom Med. 1990;52:320-336.
5. Robertson D, et al. Effects of caffeine on plasma renin activity, catecholamines and blood pressure. N Engl J Med. 1978;298:181-186.
6. van Dam RM, Hu FB. Coffee consumption and risk of type 2 diabetes: a systematic review. JAMA. 2005;294:97-104.
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