[Peak bone mass of Icelandic women and associated factors.].
OBJECTIVE
The aim of this study was to evaluate at which age peak bone mass is reached among Icelandic women. Previous studies on this subject have been conflicting indicating that this might be reached sometime between the age of 16 and 35 years. We have also analyzed associated nutritional and physical factors which might be of use for preventive measures against osteoporosis.


METHODS
A random sample of 16, 18, 20 and 25 years old women in Reykjavik were invited, altogether 335 women participated. Bone mineral density (BMD) was analyzed by Dual Energy X-ray Absorptiometry (DEXA) in the lumbar spine, hip, forearm and total skeleton. Calcium, protein and vitamin D intake was assessed by a semiquantitative food frequency questionnaire. The level of 25-OH-vitamin D in serum was measured by a radioimmunoassay. Physical activity was assessed by a questionnaire. Multivariate analysis was performed by multiple linear regression.


RESULTS
Maximal bone mineral density was reached for total skeleton, hip and forearm at the age of 20 years, BMD for the lumbar spine was 1% higher at the age of 25 than at 20 years but this was not statistically significant. No significant association was found between the calcium intake and BMD except in the subgroup of 18 years old women with calcium intake below 1000 mg/day. 25-OH-vitamin D levels were low (<25 nmol/L) in 15-18.5% of the groups but still no significant relationship was found with the bone mineral density. The strongest correlation was found between total BMD and the lean mass (0.38-0.53, p<0.01) but physical activity was also a significant factor in the age groups 16-20 years. About 25-30% of BMD variability can be attributed to these modifiable factors.


CONCLUSIONS
Peak bone mass seems to be reached at the age of 20 and measures to increase it should therefore be emphasized before that age. Our results indicate that modifiable factors, especially lean mass and physical activity, are of considerable importance in the attainment of peak bone mass in women.
Sigurdsson
G
G
Valdimarsson
O
O
Kristinsson
J O
JO
Stefansson
S
S
Valdimarsson
S
S
Knutsdottir
H B
HB
Andresdottir
T
T
Franzson
L
L
Steingrimsdottir
L
L