Thursday March 5 2009
Beer and wine drinkers had stronger bones than those who don't drink
A couple of glasses of beer or wine every day is good for your bones, The Sun reported. The Daily Express also covered the story, saying scientists found stronger associations between higher bone mineral density and beer and wine drinkers compared to spirit drinkers. However, the scientists also warned that binge-drinking damages bones and makes them weaker.
This research concluded that there is a stronger association between bone mineral density (BMD) and beer or wine intake relative to drinking spirits, and this indicates that bone health is affected by ingredients other than alcohol. It should not be interpreted to mean that alcohol should be drunk for stronger bones. The results that found an assocation with higher BMD are based on an analysis that only included some of the study participants. In this case, a cautious interpretation of the results is warranted.
Where did the story come from?
The research was carried out by Professor Katherine L Tucker from the Jean Mayer US Department of Agriculture Human Nutrition Research Centre on Aging at Tufts University in Boston, and colleagues from the US, UK and Thailand. The work was supported by several grant bodies, including the United States Department of Agriculture, the National Institutes of Health, and the National Heart, Lung and Blood Institute. The study was published in the peer-reviewed medical journal The American Journal of Clinical Nutrition.
What kind of scientific study was this?
This was an analysis of data from a cohort study, which investigated how different classes of alcoholic drink might affect bone. The researchers say that a previous study in older women found that moderate alcohol intake was associated with increases in bone density, and was therefore protective against fractures caused by osteoporosis. Alcoholism is already known to have negative effects on bone.
The researchers had data from the population-based Framingham Offspring cohort study. This study originally began in 1948 and aimed to look at risk factors for heart disease. In 1971, the adult children of the original participants and their spouses were recruited to take part in further studies, which consisted of a series of questionnaires, an examination and tests every four years. In the fifth and sixth study visits (covering the periods 1991–1995 and 1995–1999), there were 2,919 participants (1,280 men and 1,639 women, aged 29–86 years) with bone mineral density (BMD) measurements available. It is this data that the researchers analysed. The researchers had complete data on the alcohol intake and bone density at three hip sites and the lumbar spine in 1,182 men, 1,289 postmenopausal women and 248 premenopausal women, aged between 29 and 86 years.
The participants usual dietary intake was assessed by a validated 126-item food frequency questionnaire. At the two visits, one in the early 1990s and the other in the late 1990s the participants were asked to complete the questionnaires for their intake throughout the previous year. The average intake from the two questionnaires was used to estimate servings of beer, wine and spirits (liquor) per day. The servings were small by present standards: one serving represented a 356ml glass, bottle, or can of beer, one 118ml serving of wine (red or white) or one 42ml shot of spirits.
A range of other details were collected to allow the researchers to adjust for these in their analyses. These included age, sex, smoking, use of osteoporosis medication, BMI, height, physical activity, and intakes of calcium, vitamin D, magnesium, protein, as well as total energy intakes.
The average age of the participants was 61 years for men, 62 for postmenopausal women, and 48 for premenopausal women. Most people were overweight, and few were smokers.
The researchers also estimated the participants’ average silicon intake from food, beer and wine. They were interested in this because silicon is found in a number of foods, cereals and drink including mineral water and beer. The silicon in beer is found in the form of orthosilicic acid, which is readily absorbed by the body and originates from the husks of barley. The silicon intake was calculated from the dietary questionnaires data by taking average values (mg of silicon) for each food item and adding these together to obtain total silicon intake per person per day.
What were the results of the study?
The researchers reported that the men in their study were predominantly beer drinkers, whereas women were predominantly wine drinkers.
Men who consumed one to two drinks a day of total alcohol or beer had greater bone density at the hip (4.5%) than the non-drinkers (3.4%). Postmenopausal women who drank more than two drinks a day of total alcohol or wine had significantly greater bone density at the hip and spine (8.3%) than non-alcohol drinkers (5.0%).
Men who drank more than two drinks a day of spirits had significantly lower bone density at the hip (3.0%) than those who drank one to two drinks a day of spirits (5.2%).
After adjusting for silicon intake, all intergroup differences for beer were no longer significant. The differences for other alcohol sources remained significant.
The researchers note that power was low, meaning that the study was too small to analyse the premenopausal women separately, and the associations were not significant.
What interpretations did the researchers draw from these results?
The researchers say that this is the first study to look at bone density and intakes of different classes of alcoholic beverages in men and post- and premenopausal women.
They say that the results support earlier observations that moderate alcohol intake may protect BMD in postmenopausal women and older men. The benefits are most apparent from beer and wine, which suggests that factors in conjunction with ethanol may be having the protective effects.
They say that “silicon appears to mediate the association of beer, but not that of wine or liquor, with bone density” and suggest areas that could benefit from further investigation.
What does the NHS Knowledge Service make of this study?
The interpretation of this study and any implications for those who drink alcohol are complex. There are anomalies in the findings, which appear to counter the view that alcohol is “good for bones”. For example:
- The effect appears to differ between men and women.
- The effect seems to be different for women before and after the menopause.
- The effect varies according to different types of alcohol.
- Part of the effect can be removed if a statistical adjustment for silicon content of food and drink is made.
- While there are some significant differences between the groups (such as between those men drinking two or more glasses of alcohol compared to no alcohol), when the data was analysed for the trend (i.e. whether increasing alcohol consumption overall is associated with increasing bone density) many of these overall trends are no longer significant. This means that the relationship is probably not a simple linear one between alcohol and bone density.
Although it is possible to speculate about the reasons behind these associations, it is better in principle to interpret these results with caution. This is usually the case with studies like this, which demonstrate a mixture of significant and non-significant effects when the data is cut into small sub groups. Caution is particularly important when some of these sub groups show a benefit for alcohol in terms of bone density (beer in men) and some show a harm (spirits for men, but not women).