Vitamin D: A Seasonal Supplement


As many of you know by now, vitamin D is an important nutrient for our health. Vitamin D serves a primary role in bone health, as it is necessary for the effective absorption of calcium. Without sufficient calcium absorption, bones are not strong and dense. Having low bone density increases our risk of osteoporosis in later life, as well as increasing our risk of poor mobility and fractures when we fall.

Vitamin D is often referred to as the sunshine vitamin, as our primary source of vitamin D is from the action of sunlight on our skin, which synthesises the vitamin. Food sources of vitamin D are limited to certain mushrooms and products that have been fortified with vitamin D. Therefore, it is almost impossible to obtain sufficient vitamin D through our diets.

In the last few years, the vitamin D recommendations have changed and now all adults are advised to take a 10 microgram supplement of vitamin D from late October to May every year.

Why did the recommendation change?

It was previously thought that the vitamin D we synthesised during the summer months would last throughout the winter- vitamin D is a fat soluble vitamin, meaning it can be stored in the body. However, more recent research has found some issues with that assumption.

The above assumed that everyone was outside for 10 minutes during peak sunlight everyday during the summer months.

Of course that wasn't and isn't the case, many people are unable to get outside during the work day, particularly at peak sunshine.

It assumed that there was sufficient sunlight throughout summer months at our latitude.

Never mind finding the time to get outside, what about the weather?! For many of us, summer days are frequently overcast and rainy, meaning there isn't enough sunlight to synthesise vitamin D. Weather varies so much by geographical area that those in the most northerly counties of Ireland and the UK are at risk of very low levels of vitamin D, compared to their southern counterparts.

There is some research comparing vitamin D levels in individuals from Surrey in the south of England and people in Aberdeen in Scotland. Researchers in the study found significantly lower vitamin D levels among participants in Aberdeen during summer and winter months, indicating a significant difference in sunlight and vitamin D even within the UK.

It assumed that people had exposed some skin during their 10 minutes outdoors.

Some people don't realise that being in the shade, being covered by loose clothing and wearing suncream all prevent vitamin D absorption. Did you know that SPF can block up to 97% of vitamin D sythesis? (Of course many of these measures are taken to preserve skin health, which is important too!)

So, after reviewing all the evidence, the new guidance was developed!

10micrograms every day from October-May.

Important notes about vitamin D supplementation:

  • If you choose to take it in a tablet form, please take alongside or after a meal. As mentioned above, vitamin D is a fat soluble vitamin so it will be more effectively absorbed with food.

  • If you choose a spray form, you do not need to take it alongside food as it is absobed directly into the bloodstream. If you are bad at remembering to take tablets, I recommend the spray- leave it on your desk or in your car so you can don't forget!

  • Any brand will do- people often ask if any brand is best, but with vitamin D whatever is best value and available in shops you have access to is perfect.

  • If you already take a multivitamin, you may already be taking enough vitamin D. Many multivits now contain 10 micrograms of vitamin D, so no need to buy another supplement.

There are certain groups of the population at a higher risk of vitamin D deficiency, who should consider supplementing all year:

  • Those with darker skin pigmentation- darker skin has a higher level of melanin, which makes it more difficult for the skin to produce vitamin D -> meaning those with darker skin need longer exposure to sunlight to get the same amount of vitamin D.

  • Those in larger bodies- those with higher levels of body fat appear to have lower levels of vitamin D, with some research suggesting that body fat uses up some circulating vitamin D.

  • Those who cover up at all times- if you cover up with clothing or suncream at all times outdoors, it is unlikely that you will obtain sufficient vitamin D.

  • Those who are hospitalised or institutionalised- again, if you have to be indoors most of the time, you just aren't going to get enough sunlight.

  • The elderly- older people seem to be less effective at producing vitamin D, possibly related to lower levels of 7-dehydrocholesterol in the skin of older adults. 7-dehydrocholesterol is necessary in the production of vitamin D.

Take home message:

EVERYONE should supplement vitamin D during the winter months and some groups should supplement all year.

When choosing a supplement, look for one that is 10 micrograms/day and choose any brand. Spray and tablet form options are widely available.

Want to watch me rant about vitamin D? Check out below!

Lots of love,

Little O x

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