The study, led by Professor Ian Reid from the University of Auckland's Bone Research Group, found taking vitamin D supplements does not improve bone mineral density in adults with a normal Vitamin D level.
Professor Reid and his colleagues conducted a systematic review and meta-data analysis of the effects of vitamin D supplements on bone mineral density. The data from more than 4000 healthy adults in 23 randomised trials was analysed and the results published this week in leading medical journal, The Lancet.
The study found taking vitamin D supplements did not improve bone mineral density at the hip, spine, forearm, or in the body as a whole.
"Most healthy adults do not need vitamin D supplements," Professor Reid said.
"Our data suggest that the targeting of low-dose vitamin D supplements only to individuals who are likely to be deficient could free up substantial resources that could be better used elsewhere in healthcare.
"This systematic review provides very little evidence of an overall benefit of vitamin D supplementation on bone density.
"Continuing widespread use of vitamin D for osteoporosis prevention in community-dwelling adults without specific risk factors for vitamin D deficiency seems inappropriate."
Analysis of the data from the 23 studies did not identify any effects for people who took vitamin D for an average period of two years, apart from a small but statistically significant increase in bone density (0.8 per cent) at the femoral neck. According to the authors, such a localised effect is unlikely to be clinically significant.
"In North America and Europe particularly, more than half the adult population have their vitamin D level assessed and take vitamin D supplements," Professor Reid said.
"Some advocates have suggested that the indicator level for needing vitamin D supplements has been quite high.
"We believe that vitamin D supplements are only indicated for people with very low levels, such as those who are frail, are confined rest-home residents, or women who are veiled, and some dark skinned people.
"This review study suggests that the high use of vitamin D supplements by most healthy adults is a waste of money and resources."
Others at risk of vitamin D deficiencies, such as children without access to a conventional diet, especially dark-skinned children, may need vitamin D supplements to avoid conditions such as rickets that affects the growing skeleton causing bowed legs and knock knees.
"Most healthy adults … who live a normal, active life and get out regularly for activities such as walking, shopping and gardening, get vitamin D from the sun, and do not need vitamin D supplements," Professor Reid said.
"We do know that maintaining good blood vitamin D levels is important for promoting absorption of calcium from the diet.
"Very high levels of Vitamin D may have the opposite effect, and take calcium out of the bone and weaken the skeleton. There is a sweet spot in the middle, where not too much and not too little is a good level."
