DR MICHAEL MOSLEY: I don't believe in supplements - except this one, which I've now started to take all year round…

On the whole I’m not a fan of taking lots of supplements as I think you can get most of what you need from a healthy diet.

But I do make an exception for vitamin D. And with recent studies showing that high doses may not only reduce your risk of colon cancer, but also dementia, I’m now taking a higher than usual dose — and I’m also taking it all year round.

During the winter months, when the sun is weak, I’ve always followed NHS advice and swallowed a daily tablet, because I know vitamin D is so important for a whole host of reasons.

But usually by this time of year, when the sun is strong and summer is well on its way, I stop taking it. After all, I eat a lot of oily fish and eggs, both rich in vitamin D, and I also go outside for lots of walks, so my vitamin D levels should be well topped up.

However, this year I am going to keep taking those supplements.

Studies show our bodies become less effective at absorbing vitamin D from food and sunlight as we age, and that is why Dr Michael Mosley says he's taking supplements year round

That’s partly because, surprise surprise, each year I get older and studies have shown that as we age our bodies become less effective at absorbing vitamin D from food and our skin also becomes less efficient at converting sunlight into this nutrient.

That, and the fact older people tend to spend more time indoors or in the shade, means that vitamin D deficiency is very common in the over 60s, even in the summer months, particularly if you have darker skin.

But what dose should you take? That’s where things get more controversial. While the NHS suggests you stick to 10 micrograms (mcg) — or 400 international units (IU) of vitamin D a day, the National Institutes of Health in the U.S. recommends 15 mcg — and 20 mcg if you’re over 70.

I take 25 mcg (1,000 IU), which is within the limits of what’s considered safe (anything under 100 mcg a day for adults or 50 mcg for children, according to the NHS) but closer to the sort of doses studies show you need to take to ward off infections, cancers, and maybe even dementia.

Since its discovery in the 1920s, vitamin D’s best-known role has been to keep your bones healthy by increasing the body’s absorption of calcium.

In recent years, scientists have discovered that there are vitamin D receptors in nearly all our cells, suggesting that its usefulness extends far beyond the bones.

But there’s mounting evidence that to enjoy the benefits in these areas, such as preventing colon cancer and maintaining brain health, you need bigger doses than routinely recommended.

For instance, when it comes to cancer, a very recent study, published in the journal Science, showed that one of the ways taking large doses of vitamin D might work is by boosting the sort of gut bacteria that are particularly good at preventing the growth of bowel cancers. When researchers at the Francis Crick Institute in London gave mice a diet rich in vitamin D it boosted levels of Bacteroides fragilis — and higher levels of this bacterium protected them better against colon cancer.

Although there is currently no clear evidence that taking high-dose vitamin D has the same impact on the human gut, there are trials under way looking at using it to treat colon cancer.

In 2017, for example, a trial of 139 patients with advanced colon cancer who were undergoing chemotherapy, found that those on a high dose of vitamin D (100 mcg) were 36 per cent less likely to have died, or seen their disease progress, over the course of the two-year study than those on a low dose (10 mcg). Encouraged, the team is carrying out a bigger, longer study looking at whether high-dose vitamin D can help slow down or even prevent the spread of the disease.

Meanwhile, evidence is also mounting for the impact of vitamin D on delaying dementia.

Last year there was a fascinating study by Exeter University where they looked at the brains of more than 12,000 people taking part in the U.S. National Alzheimer’s Coordinating Center (a project collecting data on the disease).

At the start of the study the patients were an average age of 71 and dementia-free — and just over a third (37 per cent) said they were taking vitamin D supplements regularly. Fans of vitamin D will be pleased to hear that over the next ten years those taking the supplements were 40 per cent less likely to get dementia.

This may be because vitamin D has been shown to help prevent the build-up of two proteins in the brain, amyloid and tau, which have been linked to dementia. It also helps reduce inflammation, another trigger for dementia.

Although compelling, this wasn’t a proper randomised controlled trial — where people taking the supplement would be compared with a placebo group — and the patients were all on very different doses, which makes it hard to interpret these results.

So, Exeter University researchers have been running a trial with patients at risk of developing dementia, which will include randomly allocating them to a high-dose vitamin D (100 mcg) supplement or a placebo. I will let you know when the results are published.

In the meantime, take a supplement if you need it (obviously ask your doctor about the appropriate dose, particularly if you have existing health problems) and take full advantage of the vitamin D boost you get in the summer months, by spending at least ten minutes a day outside — with your sleeves rolled up. 

Walking down stairs can help your heart

When I’m at an airport or shopping centre I’m always surprised (and disappointed) by how many people stand on the escalator, even when it’s going downwards.

All I can say is that you’re missing out on the chance to give your heart a good work out and, potentially, extend your life. That was the conclusion of a recent review presented at a conference of the European Society of Cardiology.

Based on data from 480,000 people, it found those who regularly climb stairs were 39 per cent less likely to die from a heart attack or stroke, and 24 per cent less likely to die from any cause. This is because it’s a relatively intense exercise that quickly gets your heart racing.

It’s even more beneficial walking down the stairs — in a 2017 study by Edith Cowan University in Australia, overweight women either took a lift to the sixth floor and then walked down, or walked up and took the lift down, twice a week. After a fortnight those who walked down saw the biggest benefits in balance, bone strength and blood pressure — probably because going down stairs means your muscles have to work harder to stop you falling.

What to do about that lingering cough

You may have noticed, there is an annoying, lingering cough going round. I caught it a couple of weeks ago from my brother-in-law, who’d had it for at least three weeks, and who’d in turn caught it from his wife.

This one keeps me awake at night and doesn’t show any signs of getting better. The problem is I don’t really believe in the effectiveness of over-the-counter remedies (there is no proper evidence that cough medicines work) — but in desperation I resorted to cough syrup and a zinc supplement. Neither has so far done any good. I was particularly disappointed by the zinc, as studies have suggested that supplements can shorten a cold and reduce coughing by up to 46 per cent. (Though that only seems to apply if you take them within 24 hours of developing symptoms, so I’ve probably missed that boat.)

If you’re experiencing a similar cough, I’d suggest drinking plenty of water and the occasional hot lemon and honey (honey helps soothe the throat, while lemon has anti-inflammatory properties). The NHS says see your doctor if a cough persists for longer than three weeks.

Set a thief to catch a thief is a well-known saying which, fortunately for us, also seems to apply to bacteria. A new study by the University of Bonn, in Germany, found that a common type of skin bacteria, Staphylococcus, kills other bacteria by injecting a chemical that dissolves their cell membranes.

The idea is this could be harnessed to create a new antibiotic, which is exciting given that many bacteria are now resistant to antibiotics — including the first truly effective antibiotic, penicillin, which saved my life as a baby when I caught pneumonia.