Smoking
People who smoke have lower bone density than non-smokers. The
impact of smoking is multidimensional: in adolescence it causes
reduced peak bone mass and also affects exercise levels, absorption of
nutrients, BMI and blood supply to bone. At a cellular level, nicotine or
other chemicals from cigarette smoke reduce osteoblast activation and
increase osteoclast activity, both directly and via inhibition of oestrogen
and (in males) androgens.