Why eating a mackerel a day means you don’t have to parade down Euston Road in your underpants during winter in a bid to generate some vitamin D was just one of the pieces of information to come out of a talk on the ‘sunshine vitamin’ this week.
Vitamin D, or the ‘sunshine vitamin’, is proving to have much wider-reaching implications than anyone had realised until fairly recently – with research revealing connections between it and diseases as diverse as asthma, TB and cancer.
As people munched on their sandwiches during the lunch-hour lecture, Dr Martineau, senior lecturer in respiratory infection and immunity at Barts and the London Medical School, spoke about an experiment he conducted on vitamin D and tuberculosis.
The study first took blood samples from people, and then infected these samples with TB. The people were then split into two groups, with one given vitamin D and the other a placebo, with the whole investigation a double-blind (where the researchers conducting the experiment do not initially know which group is given which tablet).
After taking another blood sample, and infecting the second sample with TB, Dr Martineau said that “the remarkable finding” showed that those with vitamin D were more able to stop the growth of the tuberculosis bacteria than those who were given the placebo.
Links between vitamin D were now being made with a whole range of other diseases, but Dr Martineau said that more studies needed to be done before scientists could say that the changes were down to the vitamin itself, rather than other factors.
However, with TB on the increase in the UK population, which Dr Martineau put down to higher incidences of HIV and migration from areas where tuberculosis is more common, the findings are generating a lot of interest in the sunshine vitamin.
Vitamin D is formed when the skin is exposed to ultraviolet B light from the sun or artificial sources, and reacts with 7-Dehydrocholesterol, converting it into the vitamin.
According to Dr Martineau, serious vitamin D deficiency in the UK is most common in people who do not eat much fish or who have more pigmented skin, as this blocks a lot of ultraviolet B light.
However, vitamin D deficiency appears to be on the increase, which has been put down to being indoors more and therefore not having enough exposure to sunlight, because of changes in our lifestyle.
Mild or moderate vitamin D deficiency in the UK is “almost ubiquitous” during the winter and spring, said Dr Martineau, but sadly a summer of sunbathing won’t mean we can “stock up” on the vitamin.
“Unfortunately no,” said Dr Martineau. “The effects of vitamin D are long lasting, but not that long lasting.”
However, he disagreed with the suggestion that there is a conflict between those who advocate putting on plenty of suncream and avoiding the sun, and the need to get some exposure in order to make vitamin D.
“I myself don’t see any particular conflict because in the UK, even if I walked down the Euston Road in my underpants, you are not going to take much vitamin D at all in the winter months.”
On the other hand, he said, there is a risk that by trying to up one’s vitamin D quota by soaking up some rays, the risk of skin cancer also increased, and there was no way of creating a sunblock that would filter out the ‘bad rays’ and let in the ‘good ones’.
“The ones that are doing the good are doing the harm,” he explained. “So you either have them or you don’t.”
Instead, Dr Martineau said it was better to take vitamin D supplements than relying on the sun, but said that the government’s guidelines on vitamin D intake were too low.
But he put this down to the fact that “the jury is still out on whether having much higher levels of vitamin D are beneficial.”
Can you OD on vitamin D? As with most things, the answer is yes, but Dr Martineau said that you would have to take a great deal in order to have too much, and it would most likely result from someone making a 10-fold mistake when taking a very high dosage anyway. He explained that overdosing on vitamin D increases levels of calcium, causing kidney damage.
Dr Martineau, it seemed, was certainly practising what he preaches, by taking vitamin D supplements at a level equivalent to eating five mackerel filets a day.
In other words, ‘a mackerel a day keeps vitamin D deficiency away’ – maybe not particularly catchy, but a good rule of thumb all the same.