VITAMIN D AND IMMUNE HEALTH

Vitamin D is best known for its role in keeping bones strong and healthy, which it does by increasing the uptake of calcium and phosphorus from food. Some studies have also suggested that vitamin D levels may lower the risk of colon and breast cancers, while others have suggested it may play a role in protecting against cardiovascular disease, diabetes and autoimmune conditions.

However, it is vitamin D’s potential role in fighting off infections that is receiving the most attention right now, in particular, reports that the vitamin might help lessen the symptoms of Covid-19. Data from Google Trends shows four times as many people Googled vitamin D in early December 2020, compared with the same period the previous year. So, what’s the scoop on vitamin D – can it really protect our immune systems and keep us virus-free?

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VITAMIN D AND IMMUNE HEALTH

It’s long been known that vitamin D seems to play a role in modulating both the innate (immediate) and adaptive (longer term) arms of the immune system. ‘We also know that vitamin D has a unique role in making a potent antimicrobial peptide known as LL-37 in the body, which has proven antiviral activity,’ says Catherine Collins, an ICU dietitian from Surrey and Sussex Healthcare NHS Trust. One pre-pandemic review of clinical trials published in 2019 indicated that vitamin D supplements could reduce the severity of acute respiratory tract infections in hospitalised patients.

Whether this applies specifically to Covid-19 is the question researchers have been scrambling to answer. In one study, treatment of Covid-19 patients with vitamin D appeared to show a big benefit: of 50 infected patients who received the vitamin, only one required admission to ICU (two per cent), while of 26 who didn’t receive it, 13 (50 per cent) required treatment in intensive care. On the other hand, another study, this time at the University of São Paulo, Brazil, found no difference in outcomes for hospitalised Covid-19 patients. These were given very high doses of vitamin D (along with standard treatments) and had no better outcome than those who received a placebo. Collins says it’s also worth noting that in the first of these two studies (the one that showed positive results), researchers used a different form of vitamin D to the one usually found in over-the-counter supplements: ‘As this isn’t the typical form of vitamin D taken, the results can’t necessarily be extrapolated,’ she says.

LOW VITAMIN D… OR SOMETHING ELSE?

One reason why it’s so difficult to pin down whether vitamin D is an effective weapon against Covid-19 and other infections is that it’s hard to tease out the actual effects of vitamin D from several other closely connected factors. ‘What we know is that people with low vitamin D levels definitely have higher risk for bad outcomes in Covid-19,’ explains Dr F. Perry Wilson, creator of the Impact Factor science communication vlog and a Yale University professor of medicine in the US. ‘But we also know that multiple factors associated with low vitamin D levels are also associated with Covid-19 infection and severity: older age, obesity, black race, poverty and having other health conditions.
‘The bottom line is that our vitamin D level is a marker of the type of life you live and it’s really, really hard to adjust for that.’

STAY TOPPED UP

That said, it’s only ever going to work in your favour to get enough vitamin D. And now, more than ever, it pays to take the simple steps you need to stay topped up. The UK recommendation is that all adults and children get 10 micrograms of the vitamin daily. At one time it was thought that this could be obtained from sunlight (and that you’d build up enough during summer to last all year), but guidelines have changed.

INDOOR LIFESTYLES

‘Indoor lifestyles, the increasing use of sunscreen (which blocks vitamin D formation) and the fact that in Northern Europe the sun is only strong enough to stimulate vitamin D production between April and September means we need to top up levels through food and/or supplements,’ says Helen Bond, a spokesperson for the British Dietetic Association. To find out how to get the vitamin D you need, see the boxes, Foods That Contain Vitamin D and What to know about supplements.

WHAT TO KNOW ABOUT SUPPLEMENTS

As a minimum, the NHS recommendation is to take 10 micrograms/µg (400 IU) of vitamin D a day between October and March, though all year round is probably safer. Confusingly, the EU nutrient reference value (NRV) for vitamin D is 5 micrograms per day. So, the 10 microgram daily intake that’s recommended in the UK is actually 200 per cent of the NRV! Higher dosages are OK – but the NHS says don’t go above 50 micrograms (2000 I.U) a day. Keeping a check on your vitamin D levels is a good idea if you are experimenting with higher doses. You can get an NHS-approved pin prick blood test by post for £29 from www. vitamindtest.org.uk. For optimal immune health, you’re aiming for a serum 25(OH)D concentration (the biomarker of vitamin D exposure in the blood) of around 75nmol/L, but less than 150nmol/L. Too much can be toxic.

FOODS THAT CONTAIN VITAMIN D

Fresh raw salmon: 6.1 micrograms per 130g fillet Pickled (rollmop) herrings: 11.2 micrograms per 70g serving (half a small jar) Canned pink salmon: 7.9 micrograms per 105g small can Canned sardines (in tomato sauce): 4 micrograms per 120g Vit D-enriched mushrooms (e.g, Sainsbury’s Super White mushroom, 300g for £1.20): 3 micrograms per 100g sauteed serving Eggs: 1.6 micrograms per egg Bran flakes (Kellogg’s): 2.5 micrograms per 30g serving (note not all cereals contain vitamin D)

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