Writing in the American Journal of Clinical Nutrition, the researchers set out to test the assumption that caffeine intake is related to the development of arterial fibrillation (AF). This belief, they said, is “fairly widespread” but there is little information to support it.
They conducted their prospective assessment using data from the Women’s Health Study, a completed randomized trial that evaluated the risks and benefits of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer. Women who participated in this study were randomly assigned to receive 100 mg aspirin every other day, 600 IU vitamin E every other day, both agents, or a placebo.
A total of 33,638 initially healthy women participated in the study. They were all under the age of 45 and free of cardiovascular disease at the start of the study.
Participants were prospectively followed for incident AF from 1993 to 2009.All women provided information on caffeine intake via food-frequency questionnaires at baseline and in 2004.
The questionnaires assessed average consumption during the previous year of a specific amount of foods, including coffee, decaffeinated coffee, tea, caffeinated cola, decaffeinated cola, low-calorie caffeinated cola, low-calorie decaffeinated cola, and chocolate. It allowed nine responses that ranged from never to over 6 times per day.
Intakes of nutrients and caffeine consumption were calculated by using the US Department of Agriculture food composition data and supplemented by food manufacturers. As part of their calculations, the researchers assumed that the content of caffeine was 137 mg/cup of coffee, 47 mg/cup of tea, 46 mg/can or bottle of cola, and 7 mg/serving of chocolate candy
Their analysis revealed that average caffeine intakes across increasing quintiles of caffeine intake were 22, 135, 285, 402, and 656 mg/d, respectively.
During around 14 years of follow-up, the researchers identified 945 AF events.
They used a number of different statistical analyses to assess the link between caffeine intake and the incidence of AF.
The researchers noted that age-adjusted incidence rates of AF across increasing quintiles of caffeine intake were 2.15, 1.89, 2.01, 2.24, and 2.04 events, respectively, per 1000 person-years of follow-up.
They found that none of the individual components of caffeine intake (coffee, tea, cola, and chocolate) were significantly associated with incident AF.
“Elevated caffeine consumption did not confer an increased risk of incident AF in this large cohort of initially healthy women,” they concluded.
“By contrast, pending confirmation by other prospective studies, the consumption of small to moderate amounts of caffeine may have a small but significant protective effect on the occurrence of AF.”
Caffeine consumption and incident atrial fibrillation in women
Am J Clin Nutr 2010;92:509–14.
Authors: David Conen, Stephanie E Chiuve, Brendan M Everett, Shumin M Zhang, Julie E Buring, and Christine M Albert