Osteoporosis and the sunshine supplement
Published on 01 October 2008
As Arthritis Research UK’s new trial looking at the relationship between vitamin D deficiency in pregnant women and their babies’ bone density gets under way, Jane Tadman looks at the role of the so-called sunshine supplement.
While most people can get most essential nutrients from a healthy diet and don’t really need the vitamins and supplements urged on them by the health pages of the tabloid press, there is one exception.
Vitamin D is mainly generated in the body by exposure to sunlight, and as the UK is virtually a sun-free zone for six months of the year during the winter, it’s not surprising that many Brits are vitamin D deficient. Darker-skinned people living in the UK are particularly at risk of being deficient and developing rickets or osteomalacia as a consequence.
Vitamin D deficiency has been linked to many different diseases from heart disease to cancer, multiple sclerosis and diabetes, and accordingly the so-called sunshine vitamin has been hailed in some quarters as a wonder supplement in countering the risks of developing these conditions.
The vitamin also plays a vital role in maintaining healthy bones and avoiding the brittle bone disease osteoporosis, as it’s needed in order for bones to absorb calcium, which plays a key role in keeping bones strong.
For the past few years scientists working in osteporosis research have increasingly found that the state of an individual’s bones in later life can be traced back to before they were even born – when they were still in the womb, in fact. A team at the Medical Research Council Epidemiology Resource Centre and University of Southampton under the direction of Professor Cyrus Cooper has published some fascinating findings about the role of vitamin D in pregnancy and its effects on babies’ bones.
Vitamin D deficiency is extremely common in pregnancy
Their research has now culminated in the UK’s first clinical trial, funded by a £652,000 Arthritis Research UK grant over three years, to find out if giving vitamin D supplements to pregnant women who are vitamin D deficient increases the bone density of their babies at birth.
Results of the trial could have a significant effect on public health policy, as, if the supplement is found to be effective, it could lead to the routine supplementation of pregnant women with vitamin D.
Vitamin D deficiency is extremely common in pregnancy, affecting up 18 per cent of white women and a far higher proportion of Asian women, according to recent studies. The Food Standards Agency recommends a ten microgram daily vitamin D supplement, but there is little evidence for the effectiveness of this dose.
However, a previous observational study by Professor Cooper’s team showed that children whose mothers were vitamin D deficient during pregnancy had weaker bones in childhood.
Those women who took vitamin D, or were exposed to more sunlight, had children with higher bone density, the study found. Women who gave birth in the spring, and were therefore exposed to less sunlight during winter months, had children with lower bone density. The crucial finding was that it was the vitamin deficiency of the mother, rather than that of the child in early life, which affected the child’s bone strength in later life.
Related, ongoing research by the team has also revealed that a combination of poor bone growth of the foetus in the womb, and diet and exercise during a child’s early life, are both important in the development of strong bones, and in avoiding osteoporosis.
However, according to Dr Nick Harvey, Lecturer in Rheumatology at Southampton University who is leading the Southampton arm of the trial, what goes on in the womb may play the more significant role in the development of healthy bones throughout life.
“This is the first randomised controlled trial to formally assess the effectiveness of prenatal intervention on the later risk of osteoporosis in the newborn offspring – to look at whether the bone mass of an individual can be modified before it is even born,” he explained.
Results of the trial will inform public health policy
“That period of very early development is potentially the cause of permanent change during the growth trajectory. Calcium intake during childhood can modify growth temporarily but it probably doesn’t have a long-term effect. It may be that what happens during the intra-uterine period can give a lifetime of benefit, so for these mothers – for all mothers - this is a really, really important study. We hope that the results of this trial will definitively inform public health policy on the use of vitamin D supplements in pregnancy.”
One hundred and eighty pregnant women from the Southampton area attending the Princess Anne Hospital will take part in the 18-month pilot study of the trial, which will then be extended to around 1,000 women recruited from centres in Sheffield and Oxford over a further two and a half years.
Women are now being recruited for the pilot study when they attend their 12-weekly pre-natal scan. Volunteers will be split into three groups at 14 weeks gestation, with one group taking 500 iu (12.5 micrograms) of vitamin D, the second group taking 1,000 iu (25 micrograms) of vitamin D, and the third group taking a placebo pill, for the duration of their pregnancy. They will be seen again at 19 and 34 weeks when they have their ultrasound scans.
After they have given birth, their babies’ bone density will be measured by DXA scan within fourteen days.
The women will also fill in questionnaires looking at what they eat, how much vitamin D and calcium they get from their diet, whether they smoke and how much alcohol they drink.
"We don't get enough sunshine in this country"
The main trial will test which ever dose of vitamin D is shown to be more effective in the pilot study, versus placebo. A subset of women taking part in the main trial will also be given light sensitive patches to measure their sunlight exposure.
Dr Harvey adds: “We don’t get enough sunlight in this country. In winter you probably won’t make any vitamin D at all – and in the summer months using sun screen of factor eight or above will significantly reduce the skin’s ability to make vitamin D. So taking supplements may well be a sensible thing to do.”
Hopefully arc’s new trial will raise awareness of the need for vitamin D among the great British public – as well as changing public heath policy for the better.