So the sun has gone, and along with it our daily dose of vitamin D. Apart from the invigorating feeling that the sun has on us, and perhaps our propensity for outdoor drinking (!), most of us know that sunlight is required for us to produce vitamin D in our skin.

But do you know, that around about now, towards the end of September, even on the sunniest of days, the sunlight won’t be much use to help us produce vitamin D in England? It’s even worse the further north you travel. Between April (ish) and the end of September there’s a chance you could receive your daily dose of vitamin D by exposing your arms to the sun for between 20-60 minutes, depending on your skin colour (fair to dark, respectively). Outside of this time we more than likely need to take supplements and, or, fortified foods.

Did you know that over a billion people Worldwide are vitamin D deficient?

Changes in our behaviour and eating habits over time, such as working indoors, commuting by car rather than by foot and ‘easy’ nutritionally-deficient food options, has meant that we’re not getting enough vitamin D.  It’s a real problem.

Why is vitamin D important?

I can hear your shout – “for bone health!” Well, obviously I can’t hear you but, you’re right if you thought this. Most of us know that vitamin D (Vitamin D3 is called cholecalciferol) is important for bone health, and severe deficiencies can lead to Rickets. Did you also know that though that Vitamin D is also very important for muscle development, growth and performance? It might also influence post-exercise repair!

Vitamin D deficiency has been reported in various patient groups, including those who are rehabilitating and vitamin D-deficient individuals show poor muscle performance. Indeed, severe deficiency is often associated with non-specific muscle aches and pains.

Correction of Vitamin D Deficiency

Correction of vitamin D deficiency by supplementation (often by high dose tablets taken in conjunction with calcium) has been shown to increase muscle performance, reduce the risk of falling in frail individuals (maybe) and reduce non-specific muscle aches and pains.

There may be an extra benefit too, which is of particular relevance in rehabilitating populations, and funnily enough in those who partake in high-intensity exercise.

Vitamin D intake is measured in micrograms (µg) or IU, with 1µg equivalent to 40 IU.

Vitamin D for Muscle Strength and Repair

I wrote a systematic review on this (“A systematic review of the role of vitamin D on neuromuscular remodelling following exercise and injuryYou can download the full paper here), it’s a couple of years ago now, but we conducted this review because understanding whether or not vitamin D status has an influence on the extent of physiologic adaptation may be particularly relevant during rehabilitation.

We know that supplementation can independently increase muscle strength in chronically-deficient populations. However, the regulatory role of vitamin D on neuromuscular remodelling and adaptation subsequent to exercise conditioning or injury had not been systematically reviewed.

We sought to understand If vitamin D deficiency is associated with sub-optimal remodelling following injury or stressful exercise, as rehabilitation often involves unaccustomed and relatively high-intensity exercise that is stressful to the neuromuscular system. This could be important in patient populations from the perspective of, for example, limiting muscle strength gains and muscle repair.

In our review we reported that vitamin D may have an important role in nerve and muscle tissue repair, but research is limited to animal models; furthermore evidence is emerging for the role of vitamin D in reducing the symptoms of muscle soreness (DOMS) following high-intensity exercise. Upshot? This research is still in its infancy, but the regulatory effect of vitamin D in recovery may be mounting.

25-Hydroxyvitamin D is measured in ng/mL (US)  or nmol/L (UK), with 1 ng/mL equivalent to 2.5 nmol/L.

Are you Vitamin D Deficient?

Despite the large volume of research into the consequences of deficiency, what constitutes deficient vitamin D levels is debated. We’ll save the lengthy debate for another time. Measured by circulating serum concentrations of vitamin D (25(OH)D), much of the literature reports:

  • 25(OH)D levels of 50 –75 nmol/L (20–30 ng/mL) as ‘insufficient’
  • <50 nmol/L (20 ng/mL) as ‘deficient’
  • Therefore we really should be aiming for levels >75nmol/L.

… Don’t forget to lock the door on your way out to Holland and Barrett!

Seriously, not that I’m giving ANY advice here, apart from check with your GP before you take anything, but if you were interested and wanted to read more, vitamin D3 as has been shown to be more effective in raising serum 25(OH)D levels than vitamin D2, and adults probably need more than the daily recommended 10 micrograms recommended by the NHS to raise and then maintain adequate levels, especially over the winter months, but that’s just my personal opinion.

Here are a few other sources of information on the sunshine vitamin:
NHS: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
The Vitamin D Society: https://www.vitamindsociety.org

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