This is the thirteenth entry in a six-week series of topics following the syllabus of my Human Nutrition & Obesity graduate summer course. Each entry offers a snapshot or principal take home message from that lecture. This lecture was entitled: You Are What You … Drink 2: Water and Alcohol. @DrTomSherman or @GUFoodStudies
1997 was a good year … this is an appropriate description of a year in which three large cohort studies were published highlighting the connection between moderate alcohol consumption and decreased risk for heart disease, angina pectoris, and myocardial infarction. Epidemiologists are fascinated with U-shaped curves and the relationship between all-cause mortality and alcohol consumption exhibits a classic U-shaped curve: as alcohol intake increases, all-cause mortality decreases to a nadir at approximately 1 drink per day, and then increases again as alcohol intake continue to rise. The increase in mortality at higher levels of alcohol consumption was easy to establish as part of the constellation of bad consequences that occur when we drink too much. Explanations for the decrease in mortality at more moderate intakes, however, required more investigation, but it had to involve a frequent cause of death in order for it to impact all-cause mortality as much as it did. Given the prominent contributions of heart disease to all-cause mortality, perhaps it should not have been such a surprise that this was where alcohol proved so beneficial, but no had dared hope that this would be case.
The data below from the Physicians Health Study, involving 22,071 healthy male physicians between the ages of 40 and 84 years, illustrates the benefits of moderate alcohol drinking on the relative risks for angina pectoris or myocardial infarction:
The multivariate relative risks are expressed relative to 1.00, with values below 1.0 as indicating a decreased risk. In parenthesis next to the relative risk is the all-important 95% confidence interval (95% CI), which tells you if the risk value is statistically significant. If the 95% CI crosses the number 1.0, the calculated risk value is not statistically significant. For example, when reading the line of data for multivariate relative risk for Angina pectoris, the reference risk for <1 drink per week is 1.00, and the risk for 1 drink per week is 1.04. This means there is a calculated 4% increased risk for angina pectoris; but the 95% CI is 0.88–1.24, which covers 1.0 in its spread, and therefore this 4% increased risk is not statistically significant. In fact, significance is not reached until 5–6 drinks per week, with a relative risk of 0.74 and 95% CI of 0.60–0.90, meaning that at this level of consumption, alcohol offers a statistically significant 26% decreased risk of angina pectoris. The risks decrease further at 1 drink per day (0.69) and further still at ≥2 drinks per day (0.44). The results are roughly similar for myocardial infarction.
Alcohol has a powerful impact on heart disease, and despite earlier assertions that red wines was most effective, it appears to be the alcohol and not the vehicle that is important. Possible mechanisms for alcohol cardioprotection are quite varied, and include, for example, improved lipid profiles by increasing HDL levels and decreasing LDL levels, decreasing platelet aggregation and the risk of blood clotting, reducing blood pressure and increasing coronary blood flow.
Alcohol consumption is not without risks, however, and chief among them for women are the increased risk of cancer, predominantly breast cancer. The results of the Million Women Study are particularly clear, for in this cohort of 1.3 million middle-aged women who attended breast cancer screening clinics in the United Kingdom, it was found that every additional drink consumed per day increased the incidence of cancer to about 15 per 1000 women up to age 75:
If there is a silver lining to this data, however, it appears that much of the risk for cancer, especially breast cancer, is associated with those women consuming inadequate levels of the vitamin folic acid, or folate. There is a complicated relationship between alcohol intake and folic acid metabolism, and much of the earlier research focused on the ability of alcohol to interfere with folate metabolism, putting alcoholics in particular at risk for severe folate deficiency and highlighting the severe consequences that might result. More recently, however, studies have focused on the possibility that folate supplementation may obviate the risks of cancer that even moderate alcohol intake imparts. Three studies have examined this issue, and all three found that supplemental folate at or above 400 µg per day eliminated the increased risk of breast cancer imposed by alcohol intake.
The big question that requires a thoughtful discussion with your physician is how best to balance the cardiovascular benefits of moderate alcohol consumption with the small, but real, risks of breast and other cancers. A rubric for decision-making will involve consideration of your family history and the other associated risks for CVD or breast cancer that you possess. For example, a woman with no family history of breast cancer, but who has an unfortunate history of heart disease, may decide that the benefits of alcohol consumption outweigh the risks. On the other hand, a family or genetic predisposition to cancer and little family history of heart disease makes the decision to avoid alcohol easy. It is that vast middle ground that can be unsettling. At a minimum, I recommend that if you are a young woman who enjoys drinking alcohol, you should take a folate supplement to ensure that you get greater than 600 µg per day.