Now that we have mentioned exercise, I found this excerp
in of all places, the Usenet newsgroup hawaii.nortle.

Regards,

David
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Bone density and lifestyle characteristics in premenopausal andpostmenopausal Chinese women.Hu JF, Zhao XH, Chen JS, Fitzpatrick J, Parpia B, Campbell TC

The relationships between bone health and various lifestyle factors were
examined in a cross-sectional study in 775 Chinese women aged 35-75
years. Bone mass was significantly positively associated with body
weight, height, body mass index (BMI) and duration of breastfeeding, but
was not significantly associated with other lifestyle variables,
including alcohol consumption, parity, age at menarche and age at
menopause after adjusting for age and body weight. A positive
association was observed in premenopausal women (but not inpostmenopausal women) for bone density with current cigarette smoking
and plasma and urinary cotinine (the major metabolite of smoking).
However, the confounding effects of other unknown factors present in
this cross-sectional study may not be excluded. Daily physical activity,
as indicated by time spent working in the fields, was found consistently
to be positively associated with bone mass (p < 0.0001). When these
women were grouped into three physical activity levels on the basis of
occupation and daily work intensity, those undertaking heavy labor also
had significantly higher radial bone mass than women undertaking light
or medium labor. These results suggest a protective effect of daily
physical activity on bone health in both pre- and postmenopausal women.