Moderate alcohol consumption -- and the key is "moderate" -- was associated with a lower risk for hip fracture and low bone density when data from 33 separate studies were combined.
Compared to total abstainers, people who drank a half to one alcoholic beverage a day were found to be 20% less likely to suffer hip fractures, while people who drank more than two drinks a day had a 39% increased risk.
Moderate alcohol consumption is generally considered one drink a day or less for women and two drinks a day or less for men.
"There is quite a bit of literature that supports the beneficial effects of moderate alcohol consumption on health, and our paper adds to that," lead researcher Karina Berg, MD, of Montefiore Medical Center in the Bronx, tells WebMD. "But it also adds to the evidence that heavy alcohol consumption is detrimental."
Specifically, drinking more than two alcoholic beverages a day was associated with an increased risk for hip fracture in the analysis, which appears in the May issue of the American Journal of Medicine.
3 Drinks Is Too Many
The studies reviewed by Berg and colleagues were not specifically designed to examine the impact of alcohol consumption on bone loss and fracture risk.
These studies are needed to better understand the risk and benefits of drinking alcohol on bone health, Berg says.
She adds that it is not yet clear how much alcohol is optimal for maximizing bone density and minimizing hip fracture risk.
A fracture-risk assessment model, recently published by the World Health Organization, lists consumption of three or more alcoholic drinks a day as a major risk factor for fractures caused by weakened bones.
But Siris says more research is needed to confirm the association.
"The benefits of moderate drinking are debatable," she says. "It may be true, as this (analysis) suggests, that in small amounts alcohol is protective against fracture. But the evidence linking excessive drinking to a higher risk of fracture is much stronger."
Estrogen May Be the Key
It is not known exactly how alcohol affects bone density. If moderate drinking does help protect bones, hormones may explain why, Berg says.
Alcohol increases circulating estrogen, which helps keep bones strong.
Whatever the mechanism, Berg says alcohol intake is only one of many factors that may influence osteoporosis risk. Family history, weight, calcium intake, estrogen exposure, smoking history, and activity level all influence risk.
"Each person has to evaluate their own risk, and no one who doesn't drink should start drinking based on this research," she says.