Auckland University researchers have dismissed the need for healthy adults to take vitamin D supplements to prevent the bone-weakening disease osteoporosis.
Their conclusion - which flies in the face of the widespread use of the supplements in New Zealand and far more so in the United States - is based on a review of 23 trials involving more than 4000 people whose average age was 59.
"Most healthy adults do not need vitamin D supplements," said Professor Ian Reid, of Auckland University, the lead author of the research paper published today in the British journal, The Lancet.
"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."
Five per cent of New Zealand adults are vitamin D deficient, according to a Ministry of Health survey, and 27 per cent have a low level but not a deficiency. There is uncertainty about the optimum level. Pharmac spends more than $1.9 million a year on state-funded prescriptions of vitamin D supplements. This does not include patients' private spending on over-the-counter supplements.
Vitamin D is needed for the absorption of calcium from food. Most of the vitamin D we need is produced in the skin from exposure to sunlight, with the remainder available from foods including liver, some fatty fish, eggs and fortified margarines and milks products. Some people, particularly those with dark skin, find it hard to get enough from sunlight, especially in wintertime in the South Island.
Doctors are mostly supposed to prescribe the supplements only to those who are at high risk of deficiency, such as elderly people who live in resthomes.
The review found little evidence of overall benefit from supplementation on bone density. The only potential benefit was a small increase in bone density at the neck of the hip joint, but this was considered unlikely to be of any clinical significance.