Though the NHS is pretty sceptical about the use of vitamin C, garlic, or echinacea supplements to prevent or speed up recovery from colds, they do reccomend all adults “consider taking a daily vitamin D supplement during the autumn and winter”.
That’s because our body doesn’t make enough of the stuff in the darker months as sunlight decreases. Vitamin D is key to keeping our bones, teeth, and muscles healthy, and can help to keep our immune system in good nick.
But a recent review published in Nutrition Reviews suggested that not all vitamin D supplements are created equal.
In fact, they write, vitamin D2 might actually reduce the vitamin D type linked to better immunity, giving the opposite effect than that for which many of us purchase the supplement.
Why might vitamin D2 supplements not be as useful for us?
A previous paper published in Frontiers in Immunology found that vitamin D2 and vitamin D3 do not seem to do the same thing in our bodies.
Vitamin D3 might be better at building the virus-fighting part of our immune system, the study found.
“We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signalling system in the body – a key part of the immune system that provides a first line of defence against bacteria and viruses,” study co-author Professor Colin Smith said.
But in conversation with the BBC, Prof Susan Lanham-New, the recent study’s co-author, said, “We were really astonished that when you give D2, the D3 levels drop below even the placebo.”
This new paper analysed the data from randomised controlled trials and found that vitamin D2 supplementation appeared to decrease levels of vitamin D3, though they stress this finding “has yet to be quantified.”
Speaking to the University of Surrey, Emily Brown, lead researcher of the study, said: “We discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect of taking these supplements.
“This study suggests that, subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2.”
More research is needed into vitamin D function
The paper highlighted the importance of learning more about the impacts of vitamin D types on our immune system – “Further research into the mechanistic and physiological function of vitamin D2 and D3 supplementation should be a priority,” it reads.
This might be of particular importance to Black and South Asian groups living at northern latitudes, the earlier Frontier paper suggested, as they are at greater risk of developing a vitamin D deficiency.
“There’s a lot more work that we now need to do because the long-term impact could be that you don’t reach the required vitamin D levels or, dare I say it, you could make the situation worse,” Prof Lanham-New told the BBC.