Thursday November 8 2007
Can regular sunshine keep you young?
Vitamin D could slow the ageing process, reported the Daily Express and other newspapers. “Sunshine vitamin is secret of youth” said the newspaper, “the sun’s rays may actually be vital for a long and healthy life”. Vitamin D is created in the body in response to sunlight and may protect against age-related diseases, reported others. The Guardian said, women “with the lowest vitamin D levels showed the greatest signs of biological ageing".
The story is based on a study in which the authors looked for a link between two blood-test results in a group of women. The study did not look at sunshine or measure its affects upon the ageing process over time. The nature of this study and the unproven links between the blood tests and the ageing processes mean that this study should be taken with a pinch of salt; deliberately exposing yourself to the sun is unlikely to provide a font of eternal youth. Indeed, the strong evidence for the harmful effects of prolonged sun exposure would make this unwise.
Where did the story come from?
Dr Brent Richard and colleagues from St Thomas’s Hospital, London, UK, and the Centre of Human Development and Aging, New Jersey, US, carried out this research. The researchers were supported by grants from a number of organisations including the Wellcome Trust, the Canadian Institutes of Health Research, and the National Institutes of Health in the US. It was published in the peer-reviewed journal The American Journal of Clinical Nutrition.
What kind of scientific study was this?
This was a cross-sectional study designed to examine the link between vitamin D levels and cell age, determined by the length of telomeres in white blood cells. Telomeres are genetic material found on the ends of chromosomes; as cells age, telomeres naturally get shorter. Therefore, the length of the white blood cell telomere is a good marker of the age of the cell: the shorter the telomere, the closer it is to death. Autoimmune disease and a range of other factors like smoking and obesity are also known to be linked to shortened white blood cell telomeres.
The researchers collected the results of two blood tests, serum vitamin D concentration and white blood cell telomere length from 2,160 women who had been recruited into the Twins UK Cohort Study, an ongoing study that includes data from pairs of twins. The length of the telomere was measured in the DNA extracted from circulating white blood cells. These were then analysed by laboratory staff who were unaware of the identity of the subjects.
What were the results of the study?
Telomere length was found to be shorter in older women. Telomeres were also found to be shorter in women with lower vitamin D concentrations. When the association between telomere length and vitamin D levels was adjusted for age, it was still shown to be positive. The researchers also looked at the relationship with other factors that they knew could have an effect on telomere length, including menopausal status, physical activity, and use of hormone replacement therapy.
What interpretations did the researchers draw from these results?
The authors concluded that “our findings suggest that higher vitamin D concentrations, which are easily modifiable through nutritional supplementation, are associated with longer … telomere length”. They went on to emphasise the potential beneficial effects of this hormone on ageing and age-related disease.
What does the NHS Knowledge Service make of this study?
This cross-sectional study of biochemical and genetic markers has several limitations, some of which the authors acknowledge.
- The cross sectional design is unable to asses whether lower vitamin D levels are the cause of longer telomere length or vice versa, or which of these came first. This would require further information from other studies.
- The selection of the two different markers, one a genetic marker and the other a biochemical marker of vitamin concentration, taken at a single point in time, could introduce errors. The concentration of vitamin D may be variable and might be affected by other factors that the researchers have not taken into account. For example, the information on whether people were taking vitamin D supplementation, and how much, was only available in 700 of the 2,160 women.
- There may have been other factors such as illness, supplement or drug use that have not been measured or considered by the researchers. These may be associated with both vitamin D levels and telomere length, and could explain the observed link.
- The study has only examined this relationship in women, who are also twins. Therefore, these findings cannot be applied to other population groups.
These results suggest that some of the headlines and stories are overstating the case for sunbathing:
- This study did not look at sunbathing. Instead, it looked at the concentration of vitamin D in a blood sample. The harmful effects of high doses of ultraviolet light on skin cells are well known, and will need to be balanced against any benefit in lower doses – if they are eventually proven.
It seems too soon to recommend any individual action except, perhaps, as the researchers do, to call for more research in this area.
Sir Muir Gray adds...
I see no reason to stop taking vitamin D; in my view, it is the only vitamin for which there is good evidence for the over 50s that it helps the bones stay strong.