VitaMins Health: Vitamin D: The “sunshine” vitamin

Dietary sources of Vitamin D are limited, with around 90% of our usual intake coming from sunlight. Does our current lifestyle and diet through the winter months provide us with sufficient resources for a long and healthy life?

3 March 2020

In this edition of VitaMins Health we focus on Vitamin D and whether action is required to combat deficiency.

Blame it on the sunshine

As discussed in our recent VitaMins health: getting clued up on flu, we see significantly more people die during the winter months than at other times in the year. The effect of winter on our health extends beyond the immediate impact on mortality. For example, when we find ourselves once again waking up, going to work and leaving the office in dark, many people are hit with seasonal affective disorder (SAD). Studies show that almost a third of Brits and a fifth of Canadians and Americans suffer what is otherwise known as “winter depression”, and the main theory is that a lack of sunlight might stop a part of the brain called the hypothalamus from working properly.

There are also potentially long-term health implications of a lack of sunlight. While we get most of the essential nutrients required to be healthy from a balanced diet, vitamin D is the one exception with 90% of our intake coming from sunlight. Dietary sources of vitamin D include oily fish, eggs and fortified foods, but there is a concern that we cannot maintain sufficient vitamin D levels from these sources alone. With reduced sunlight hours being compounded by indoor lifestyles, medical professionals believe that many people are becoming vitamin D deficient during the winter months.

Although there isn’t a consensus on what constitutes vitamin D deficiency, the Institute of Medicine define a sufficient level to be a serum 25-hydroxyvitamin D value of 50-125 nmol/L. They report that 33% of the US population have levels below this and Statistics Canada state that 32% of Canadians were below the cut off. A cross-sectional National Diet and Nutrition Survey revealed that 39.3% of UK white 19-64 year olds have levels below 25 nmol/L in the winter. People with darker skin, for example those of African, African-Caribbean or south Asian background, need even more sunlight to generate enough Vitamin D. As a result, these people may be particularly at risk, as are people who aren’t often outdoors, those in institutions such as care homes or those who regularly cover up most of their skin when outdoors.  

What’s it for?

To keep bones, teeth and muscles healthy the body requires sufficient levels of calcium and phosphate. Vitamin D is needed to absorb and regulate the amounts of these nutrients in the body. A lack of vitamin D is the most common cause of the bone disease osteomalacia, or rickets when in children, which is a softening of the bones due to impaired bone metabolism. Vitamin D deficiency is also one of the main lifestyle risk factors for osteoporosis, a bone disease characterised by a low bone mass, known as “the silent thief” as bone loss occurs without symptoms until the bone breaks.

While research is still in early days, there have been studies suggesting that vitamin D might have protective benefits against heart failure, diabetes, cancer, respiratory tract infections, autoimmune disease and even hair loss.

UV trade-off

But what about getting too much sunlight? Thus far the discussion about long term health implications of sunlight exposure has predominantly focused on skin cancer, for which UV radiation is the predominant environmental risk factor. With UV linked to other skin diseases as well as ageing effects such as wrinkling, public opinion regarding sunlight has shifted from viewing it as a necessary component for a glowing tan towards avoiding excessive exposure for long term health and beauty.

With life expectancy increasing, and people looking to remain healthy and active throughout a long retirement, risk of bone diseases such as osteoporosis may become a greater concern. Hence, vitamin D deficiency might prompt a further change in attitudes regarding UV. However, it is likely that the dangers of unprotected exposure to UV far outweigh any positive benefits of vitamin D, prompting the British Association of Dermatologists to warn against the use of sunbeds or long periods of unprotected exposure to high intensity UV.

An 11-year prospective study of 1,191 adults in a subtropical Australian community found that there was no indication that the carcinogenicity of high sun exposure can be counteracted by high vitamin D status. A study estimates that for white elderly people living in the Boston area, the exposure of face, arms, and legs two to three times per week during the summer months for 5–10 min may be a sufficient strategy to optimise the production of vitamin D while preventing risk of skin cancer. The study also states that, in Boston, exposure to sunlight between the months of November and February does not facilitate significant production of vitamin D. 

So, while sunbeds are not encouraged, there is still the problem that in places such as the UK, Canada and Northern US, the intensity of UV is so low during winter that people are becoming vitamin D deficient. In order to prevent the risk of osteoporosis and osteomalacia affecting their future health and active lifestyles, people may look to supplements as a solution to this seasonal deficiency.

Future of supplements

Vitamin D supplements are one of the only supplements that medical professionals consistently advise us to take. The UK department of health recommends that children up to the age of 4 should be given a daily supplement containing 10 micrograms of vitamin D unless they are already using instant formula which is already fortified with vitamin D. They also recommend adults take a 10 microgram vitamin D supplement if they aren’t often outdoors or if they cover up their skin when outdoors and state that everyone should consider taking supplements during the autumn or winter. The organisation Osteoporosis Canada advises year-round vitamin D supplementation for all Canadian adults.

Not everyone agrees on supplements though and some people believe them to be a waste of money and potentially harmful. With regards to vitamin D, excess levels may increase the risk of kidney stones and unlike vitamin D produced in the skin, which is biologically regulated, there is the potential that vitamin D from supplements could build up to high levels. Tim Spector, Professor of Genetic Epidemiology at King’s College London takes a sceptical view of supplements stating that “we should trust that thousands of years of evolution would cope with a natural drop in vitamin D levels in winter without us snapping our limbs.”

That being said, we are now spending much more time indoors than our ancestors ever did and, with life expectancy increasing, are we giving “the silent thief” more time to cause damage? With the UK currently on the precipice of a social care crisis, it might be time to start increasing awareness of the potential risks of vitamin D deficiency to help prevent bone weakening diseases and extend the independent lifespan of the elderly. 

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VitaMins Health: Vitamin D: The “sunshine” vitamin

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