Genetic susceptibility to lower vitamin D levels and calcium intake are not associated with fracture risk, according to a group of international researchers.
They found bone mineral density was only risk factor to have a major effect on fracture risk. They said their findings add to the ongoing debate over the benefits for the general population of vitamin D supplementation, which is recommended by clinical guidelines to prevent fractures.
“Vitamin D levels had no protective linear effect on fracture in community dwelling individuals”
The findings, published in the British Medical Journal, also back recent trials that have failed to consistently demonstrate a beneficial effect of supplementation for people living in the community.
The researchers assessed 15 risk factors thought to be associated with osteoporotic fractures – including vitamin D levels, calcium intake, fasting glucose levels, age of puberty, age at menopause, diabetes and rheumatoid arthritis, using genetics.
First, they analysed the results of genome-wide association studies (GWAS) to evaluate the influence of genetic variation on fracture risk.
Using data from 37,857 fracture cases and 227,116 controls, they identified 15 areas on the chromosomes associated with fracture risk.
They then replicated their findings in 147,200 fracture cases and 150,085 controls. All 15 of the areas were linked not only to fracture risk but also to bone mineral density.
The researchers then examined the association of 15 genetic variants – each representing an individual clinical risk factor for osteoporotic fracture – against fracture risk.
It showed that only bone mineral density had a clear effect on fracture risk. None of the other risk factors tested had a major causal effect on fracture risk.
Older individuals at high risk of fractures often have low vitamin D levels, resulting in fracture prevention guidelines suggesting the use of vitamin D supplementation in the general population.
“Our analyses showed that vitamin D levels had no protective linear effect on fracture in community dwelling individuals,” said the researchers.
Likewise, they found no evidence for a protective effect of sustained intake of dairy derived calcium on fracture risk.
“Our findings are a reminder that clinically relevant changes in most of these risk factors are unlikely to result in large differences in fracture risk,” stated the researchers.
The results also “provide guidance for the design of future clinical trials on interventions that are more likely to be successful in reducing fracture risk”, they said.