Ain’t no sunshine. Better take vitamin D?

Vitamin D hit the headlines last week following the publication of a new review that revealed the supplements of the so-called sunshine vitamin can help to reduce the risk of colds and flu.  While the benefits of vitamin D for bone and muscle health are indisputable, could supplements potentially ward off the winter sniffles as well?

What is vitamin D?

Rather than a true vitamin, vitamin D is actually a pro-hormone.  When it is converted to its active form in the liver and kidney, it acts as a hormone to regulate the levels of calcium and phosphorus in the body.  Both these minerals are important in keeping bones healthy and calcium also plays a role in muscle contraction, so vitamin D is essential for bone and muscle function.  Deficiency in vitamin D can cause weakened bones, potentially resulting in rickets in children and a condition called osteomalacia in adults.  It can also result in weakened muscles.  The results of prolonged vitamin D deficiency can therefore include painful and deformed or weakened bones in growing children with a greater risk of broken bones; bone pain, muscle weakness and increased risk of fracture in adults and an increased risk of falls.

Where can I find vitamin D?

Our skin naturally produces vitamin D when it is exposed to UVB sunlight.  During the summer months (April to September) the sun is high enough in the sky and strong enough for sufficient UVB rays to make it through the earth’s atmosphere to cause this natural reaction, when we expose our skin to sunlight.  It was previously thought that the sun that we experience throughout the summer was sufficient to ensure we had enough vitamin D stored to last us through the winter months.

Last year, the Scientific Advisory Committee on Nutrition (SACN), an independent panel of experts that advise Public Health England, produced a report that concluded that many people do not maintain sufficient stores of vitamin D to supply the body over the winter months.

So what of dietary sources?  Unfortunately, there are few foods that are good sources of vitamin D.  Eggs, oily fish, liver and red meat contribute but many people avoid a lot of these foods or simply don’t eat enough.  Some foods, such as margarine and breakfast cereals are fortified with vitamin D and some mushrooms, grown under special UV lamps can be a good source.  But how much would you need to eat a day to get enough (taken from the British Nutrition Foundation’s resource page).

• 1 salmon or mackerel fillet
• 2 tins of sardines
• Almost a kilo of roast lamb
• 64 rashers of bacon
• 6 large eggs
• 7 bowls of fortified breakfast cereal
• 12 servings of margarine (if you spread 10g on your bread)

What is the current Government advice?

In light of the findings from the SACN report, Public Health England advise that all healthy individuals (including pregnant and breastfeeding women) over the age of 4 years take a supplement of vitamin D, providing 10 micrograms a day, in the winter months (October to March).  Children between 1 and 4 should also be given a supplement providing up to this amount, as this was deemed to be safe by SACN.  Babies under 1 year should be given drops of vitamins A, C and D, providing 8.5-10 micrograms of vitamin D a day, unless they are consuming 500ml or more of infant formula, which is itself fortified with vitamins and minerals, including vitamin D.

Particularly vulnerable individuals are encouraged to take a supplement of vitamin D, again providing 10 micrograms a day, all year round.  These include all those who may not get enough sun in the summer months, for example, older people in care homes or people who are housebound, those who cover up a lot of their skin for cultural reasons or those with darker skin tones.

What are the findings of the new report?

The systematic review, published in the BMJ, found that there was a small but significant reduction in the risk of upper respiratory tract infections (colds and flu) in those taking vitamin D supplements daily or weekly.  This was particularly the case for those with a prior deficiency in vitamin D and for children.  Now it is well established that vitamin D is required to support the normal function of the immune system (there is even an EFSA-approved health claim).  However, SACN concluded that there was not sufficient evidence to support that vitamin D specifically reduced the risk of colds.

So should I take a supplement?

This new research is encouraging and for some population groups, who may be deficient in vitamin D owing to reduced sun exposure, and for children, a supplement may well help to reduce the risk of colds.  For the healthy general public, the absolute reduction in risk of colds is very small.  An editorial in the same issue of the BMJ highlighted that the actual reduction in risk was only 2%.

Given the current advice to take a supplement of 10 micrograms of vitamin D a day during the winter months (or year round for at-risk individuals) for bone and muscle health, there is no need to further update this advice.

We should also try to get out in the sun (when it appears!) as much as possible during the summer months.  While it’s important to practice safe sun care, wearing a sunscreen will reduce the action of the UVB rays on the skin, so around 15 minutes in the sun without suncream should be sufficient to permit vitamin D synthesis without risk of burning.

In summary, get some sun, include sources of vitamin D in your diet and take a supplement in the winter months to support bone and muscle health.  If you get fewer colds then that’s an added bonus!

Supplements image from https://unsplash.com/@freestocks

Sunrise image from https://unsplash.com/@jakegivens