Fetal programming and childhood factors have been associated with serious adult health risks, such as obesity, heart disease, and cancer.
The researchers monitored the health of 171 men and 218 women, all of whom were part of the Newcastle Thousand Families Birth Cohort Study.
This study collected comprehensive information on birth and childhood factors, and has regularly tracked the health of 1000 babies born in May and June 1947 in Newcastle upon Tyne, north eastern England.
Of the original cohort, 832 adults were traced at the ages of 49 to 51. Of these, 389 (171 men and 218 women) completed a detailed health and lifestyle questionnaire and underwent tests to gauge bone mineral density (BMD) of the hip, spine, and top of the thigh bone (femur).
For men, birthweight was a significant factor for bone size, while birthweight was a significant factor for BMD. For women, the size of the head of the thigh bone was associated with increasing socioeconomic advantage at birth.
But all in all, these factors accounted for less than 7% of the variation in BMD in men and for less than 1% in women.
For both sexes, almost half of the variation in BMD explained by early childhood factors was mediated through weight in adulthood
Increasing numbers of pregnancies lowered hip BMD in women. Vitamin C intake also seemed to be important for men.
And, overall, adult lifestyle and body size accounted for most of all the variation in the indicators of bone health at age 49-51 in both sexes. Adult weight was a particularly important factor for women, and accounted for 25% of the variation in BMD.
The authors conclude that while "birthweight does seem to influence skeletal growth, adult lifestyle and body size seem to be the most important determinants of bone health in middle age in this cohort." Cutting the risk of poor bone health in middle age means adopting a healthy lifestyle, they add.