How much impact does smoking have on your bone density?

Smoking roughly doubles the risk of osteoporosis. Compared with non-smokers, smokers have an approximately 2.2 times greater risk of osteoporosis and an approximately 70% higher chance of osteopenia, a less severe form of bone density loss. That increased risk holds even after accounting for other factors such as age, sex and weight.

The more you smoke, the greater the effect. Research into cotinine concentrations -- a substance in the blood that reflects how much you smoke -- shows that the risk increases as smoking increases. There is no simple threshold above which it becomes dangerous, but there are inflection points in the data beyond which the risk jumps noticeably.

In women who smoked heavily -- more than 15 cigarettes per day -- the risk of a hip fracture was 30% higher than in non-smokers. In light smokers that elevated risk was not demonstrable. This is an important distinction, because a hip fracture at an older age has major consequences for mobility and independence.

Whether this is a genuinely causal relationship is supported by genetic research. A study that used genetic variants as a proxy for smoking behaviour found that the genetic predisposition to smoke also increases fracture risk, independently of other lifestyle factors. Notably, no direct effect on measurable bone density was found, suggesting that smoking increases fracture risk partly through pathways other than bone density loss alone.

Quitting helps, but it takes a long time before your risk declines. Former smokers who had quit less than ten years ago showed no demonstrably lower hip fracture risk than active smokers. Only after ten years of not smoking did the risk fall significantly. There are no proven treatments that specifically reverse smoking-related bone damage, so quitting remains the primary measure.