Wednesday September 7 2011
Women should drink no more than 2-3 units a day
A study has found that “middle-aged women who indulge in a drink or two a day are boosting their chance of good health in their seventies”, The Daily Telegraph reported.
This study was in 13,894 nurses in the US. Their alcohol consumption in midlife (average age 58 years) was monitored and compared with their chances of being free from major chronic disease and mental impairment in later life. Light to moderate alcohol consumption (about 0.6 to 3.75 units per day) during midlife was associated with a small (2.1%) absolute increase in the chance of being free of these conditions at age 70 compared with drinking no alcohol. The study also found that those who spread their midlife drinking over the week experienced more benefit than those who concentrated their alcohol consumption on just one or two days.
Overall, this research is consistent with other research showing that low to moderate alcohol consumption may be associated with improvements in some areas of health. However, it is important to remember that the harmful effects of drinking heavily are well established. See our Live Well pages on alcohol for the UK recommendations on consumption and other advice.
Where did the story come from?
This study was carried out by researchers from the Harvard School of Public Health and Harvard Medical School. Funding was provided by grants from the National Institutes of Health and Boston Obesity Nutrition Research Centre.
The study was published in the open-access peer-reviewed journal PLoS Medicine.
The news coverage of this story was generally accurate. The Daily Mirror report may have given readers the mistaken impression that the study looked at drinking in old age, when it actually looked at the effects of drinking in midlife on the likelihood of healthy survival in old age.
What kind of research was this?
This study examined the effect of alcohol consumption during midlife on women’s chances of being free from major chronic disease and mental impairment in later life. The researchers focused on aspects of what they called “successful ageing”, which they defined as “being free of 11 major chronic diseases and having no major cognitive impairment, physical impairment or mental health limitations”.
The authors state that previous research has found that moderate alcohol consumption reduces the risk of premature death. However, it is largely unknown whether moderate alcohol intake is also associated with overall health and wellbeing among populations who have survived to older age.
This research looked at a subset of women taking part in a prospective cohort study in the US called the Nurses’ Health Study. A cohort study is an appropriate and feasible study design for assessing the relationship between alcohol consumption in midlife and successful ageing later on.
What did the research involve?
The Nurses’ Health Study was established in 1976 when it enrolled 121,700 female nurses. Every two years afterwards the women were sent questionnaires asking them about their lifestyle and medical history.
Consumption of beer, wine and liquor at midlife (average [median] age 58 years) was assessed using a validated food frequency questionnaire. The alcohol consumption results from the 1980 and 1984 questionnaires were then averaged to determine each woman’s daily midlife alcohol use. One drink was defined as a 355ml bottle or can of beer, a 118ml glass of wine or a shot of liquor.
These same women were followed up at age 70 or older and their health status checked to see if they had “successfully aged” as the researchers put it. Successful ageing was considered to be being free of 11 major chronic diseases (including cancer, diabetes and heart disease) and having no major cognitive impairment, physical impairment or mental health limitations.
In the Nurses’ Health Study, 21,202 were 70 years or older and free of stroke in 1995-2001. These women were invited to participate in the study. The researchers excluded women who drank more than 45g of alcohol a day (5.6 units) at midlife. They also excluded women who already had chronic diseases at the start of the study; had been diagnosed with alcohol dependence, chronic liver disease or cirrhosis; had missing information on health outcomes or alcohol use; or reported having substantially reduced their alcohol consumption when asked in 1980 (as this could indicate problems with alcohol). This left 13,894 female nurses for the current analysis.
The statistical analysis took into account a range of factors that could have potentially influenced the relationship between midlife alcohol consumption and successful ageing (confounders). These were: age; body mass index; physical activity; smoking status; level of education; husband’s level of education; marital status; postmenopausal hormone use; family history of heart disease, diabetes or cancer; personal history of hypertension or high cholesterol; use of aspirin and dietary intake of fruit and vegetables, wholegrains, fish and red meat.
What were the basic results?
Of the eligible participants, 10.7% achieved “successful ageing”. A quarter of women did not drink in midlife, while 62.1% drank about one drink a day, 9.8% drank about one to two drinks a day and 9.8% drank two to three drinks a day. The vast majority of women who drank in midlife drank wine.
The researchers found that, after taking into account the influence of a range of potential confounders:
- Light drinkers in midlife (5.1-15g of alcohol per day, or 0.6 to 1.9 units) were 19% more likely to age successfully (odds ratio [OR] 1.19, 95% CI 1.01 to 1.40) than non-drinkers. The absolute difference between the proportion of women who had successfully aged who drank lightly (11.6%) compared with non-drinkers (9.6%) was small at 2%.
- A higher proportion of light to moderate drinkers in midlife (5.1g to 30g of alcohol, or 0.6 to 3.75 units per day) aged successfully (11.7%) compared with non-drinkers (9.6%). The absolute difference was 2.1%.
- Moderate drinkers in midlife (15.1-30.g of alcohol per day or 1.9 to 3.75 units) were 28% more likely to age successfully (OR 1.28, 95% CI 1.03 to 1.58) than non-drinkers. The absolute difference between the groups was 2.2%.
- There was no statistically significant benefit in those who consumed higher levels of alcohol (30.1-45g of alcohol or 3.75 to 5.6 units per day) compared with non-drinkers.
After taking into account total alcohol consumption, these differences were more pronounced in people who drank alcohol more regularly throughout the week, rather than on fewer occasions. This was demonstrated by the finding that people who drank on one to two days a week had the same chances of successfully ageing as non-drinkers. Those drinking on three to four days in midlife were 29% more likely to have successful ageing than non-drinkers (OR 1.29, 95% CI 1.01 to 1.64). Those who drank on five to seven days per week in midlife were 47% more likely to have successful ageing than non-drinkers (OR 1.47, 95% CI 1.14 to 1.90).
How did the researchers interpret the results?
The researchers state that “these results suggest that regular, moderate consumption of alcohol at midlife may be related to a modest increase in overall health status among women who survive to older age”. In addition, they say their results “suggest the potential importance of drinking pattern in the relationship between alcohol use and successful ageing”.
The results of this analysis of a large prospective cohort study of female nurses suggest that light to moderate alcohol consumption during midlife is associated with a modestly improved overall chance of being free of major chronic disease and mental impairment at 70 years of age. In addition, they suggest that those who spread their drinking out over more days of the week may be more likely to achieve successful ageing than those concentrating consumption over just a few days.
While this study has some strengths, such as its size and prospective data collection, the following issues need to be considered when interpreting the results:
- It is possible that at least some of the women who did not drink might have not done so because of ill health or alcohol problems. This would mean that the non-drinking group would be less likely to be healthy in old age as they were already sick in midlife. Although the chances of this may have been minimised by excluding people with major chronic diseases and known alcohol dependency at the start of the study, it may not have been eliminated entirely.
- There may have been residual confounding. This means that other factors that weren’t measured, such as wealth, could potentially have influenced the relationship between alcohol consumption and successful ageing. This was minimised in this study by adjusting for a large range of confounders in the statistical analysis, including educational attainment, which can give some indication of wealth. The researchers suggest that their findings should be interpreted cautiously because of this possibility.
- The research was in registered nurses of European ethnic origin. Hence, these results cannot be generalised to men or women of other ethnic backgrounds, or of different socioeconomic status, who may have different drinking patterns and health outcomes.
- As with all studies of this type, accurately assessing the level of alcohol consumed can be tricky, as it relies on people estimating how much they drink.
Overall, this research provides evidence that light to moderate alcohol consumption, in the region of one to two drinks per day, is associated with an increased chance of ageing successfully in women of European origin. This is consistent with other research showing that light to moderate drinking may be associated with improvements in some areas of health. It is more difficult to be certain that the drinking itself is causing these improvements, and not other factors.
However, it is important to remember that the harmful effects of drinking heavily are well established. The current UK recommendations are that people who drink should drink no more than three to four units of alcohol per day for men (approximately one pint of high strength larger) and two to three units for women (approximately one standard size glass of wine).