Coffee reduces risk of death by 20% (if you look at a very specific group)

The Tweet: “For women, drinking 1-3 cups of coffee a day reduces their risk of cardiovascular disease by 24%.”

“Consumption of coffee, a major source of dietary antioxidants, may inhibit inflammation and thereby reduce the risk of cardiovascular and other inflammatory diseases in postmenopausal women,” conclude researchers from the University of Oslo in a paper published in 2006 in The American Journal of Clinical Nutrition. But this doesn’t mean we should all drink more coffee to avoid heart disease.

The researchers followed 41,836 postmenopausal women aged 55-69 from Iowa for 15 years to establish how dietary antioxidants affected risk of death from cardiovascular disease. The researchers examined coffee as the primary source of dietary antioxidants, noting: “in a healthy Norwegian population coffee contributes 60% of total dietary antioxidants.” The women that consumed 1-3 cups of coffee a day had a hazard ratio of 0.76 for death caused by cardiovascular disease, compared to 0.81 and 0.87 for 4-5 cups and greater than or equal to 6 cups per day respectively.

A hazard ratio describes the probability of death in one group compared to another. In this case the three coffee drinking groups (1-3, 4-5 and more than 6 cups per day) were compared to women who didn’t consume coffee. This means that for every 76 deaths by cardiovascular disease in the 1-3 cup group there will be 100 deaths in the non-coffee consuming group.

The quantity of coffee doesn’t improve survival chances. For the two groups that consumed greater quantities of coffee the hazard ratio increased. The researchers also recorded the hazard ratio for deaths by causes other than cardiovascular disease, which for the 1-3 cup group was 0.80, the 4-5 cup group 0.76 and greater than 6 cup group 0.79. This suggests that drinking coffee everyday reduces the risk of death due to causes other than cardiovascular disease by a similar amount, and in the case of heavy coffee drinkers by a greater amount. Perhaps this says more about non-coffee drinkers than anyone else.

However, since 2006 antioxidants are no longer the super food they were once thought to be. A meta-analysis published in 2013 of 50 studies into the effect of antioxidant supplements on prevention of cardiovascular disease found no evidence to support their use. In fact, the study found antioxidant and vitamin supplements were associated with a slight increase in the risk of angina. Studies like this show the importance of using meta-analyses to examine the efficacy of health claims and to smooth out results from studies with unrepresentative samples.

Image credit: Michael Dales (Flickr)
This post was first published on The Untweetable Truth (6/11/2014)
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