Why vitamin D production is slower in old age

by Jennifer Bowden / 22 January, 2019
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Getting our quota of vitamin D becomes more important – but more difficult – as we age.

QUESTIONIn older people, our skin becomes thinner and less protective – “like tissue paper” is a common phrase. Is the ability of skin to produce vitamin D significantly compromised as the skin ages?

ANSWER: We live in a culture obsessed with youth; advertisements for “anti-ageing treatments” are an everyday reality. And the subconscious message we’re bombarded with is entirely clear – we should fight and avoid ageing at all costs. But why? Sure, ageing brings with it a number of changes that make maintaining good health more challenging, but it would be wrong to think of it as a disease.

A more realistic and helpful approach is to focus on how we can maintain health throughout our lifespan, embrace the changes that occur in our body and look for solutions to manage their effects.

As you’ve noted, our skin changes as we age. In fact, its thickness decreases from about age 20 – so it’s a long process. And, given vitamin D production occurs in the skin, it’s valid to ask whether these changes affect production later in life.

In the top layer of your skin, the epidermis, is a plentiful supply of a compound called 7-dehydrocholesterol (7-DHC). When your skin is exposed to the sun, the ultraviolet radiation (UVB rays) causes 7-DHC to change into a precursor of vitamin D that, in turn, is converted into vitamin D, boosting our stores of the compound.

However, as we age, a number of changes affect our vitamin D production. For a start, there is a decrease in the concentration of 7-DHC in the epidermis in older compared with younger adults, and there is also a reduced response to UV light. This results in about a 50% decrease in the formation of previtamin D3 through the skin.

Ageing also leads to declining kidney function, and that, too, slows down one of the steps that converts vitamin D into the bioactive form of the compound used throughout our body.

Given vitamin D plays an important role in bone metabolism, and researchers are now looking at its role in reducing the risk of a number of health conditions – such as colon cancer, auto-immune disorders and diabetes mellitus – maintaining an optimal level of the vitamin is important at all ages.

Regardless of age, sun exposure is still a helpful way to boost our vitamin D status. Short and frequent exposure is the best way to achieve this, especially in the hotter seasons.

Between September and April, sun protection is recommended – finding shade, and wearing a hat and clothing that shades the face and neck, along with sunscreen and sunglasses – especially between 10am and 4pm. However, a daily walk is a great option, as it keeps you warm and exposes your skin to the sun: aim to be outdoors in the early morning or late afternoon, rather than during the middle of the day.

Gardening is another great opportunity to get some sun exposure.

Remember, too, that vitamin D is found in small amounts in foods such as oily fish (for example, salmon, tuna, sardines, eel and warehou), milk, milk products, eggs and liver. You can also find margarine, spreads, dairy substitutes and liquid meal replacements that contain added vitamin D.

However, vitamin D supplementation may be required for the following groups who, according to the Ministry of Health, have a higher risk of vitamin D deficiency:

  • People with naturally dark skin – including many from Africa, the Indian subcontinent and the Middle East, especially those who wear veils or clothing that totally covers them.
  • People who completely avoid sun exposure because they’ve had skin cancer, skin damage from the sun or are on photosensitising drugs.
  • People with low mobility, who are frail or housebound, including those who are bedridden or chair-bound.

These groups may benefit from vitamin D supplementation – talk to your GP if you think you might be at risk. The standard (Pharmac-subsidised) tablet prescribed in New Zealand is a single 1.25mg (50,000 international units) tablet of cholecalciferol a month.

This article was first published in the January 12, 2019 issue of the New Zealand Listener.

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