Vitamin D: Benefits, Sources & Deficiency

Approx' 1 in 5 people in the UK have low Vitamin D levels…

Strictly speaking, ‘Vitamin D’ actually refers to a group of compounds. Vitamin 'D3' is most the most commonly found as a food supplement. This is simply due to the fact the D3 is absorbed and used by the body more effectively than the other forms of Vitamin D. D3 supplements will clearly display “Vitamin D3” on the label.

Vitamin D is a vital nutrient, essential for health… and as you’ll see below, a large number of health problems have been associated with Vitamin D deficiency.

So, just like all vitamins, optimising your levels of this nutrient provides MANY health benefits.


As with all vitamins... Vitamin D is essential for health & wellbeing. The clue is in the name... "Vita" - the Latin word for life.


Potential Benefits of Optimising Vitamin D Levels

  • Healthy immune system: Simply from a general health point of view, this is obviously a very positive benefit… we all want to avoid getting ill as much as possible of course. But a strong immune system also means that you'll be less likely to miss workouts through illness. Over the course of weeks/months/years, this increased consistency in your training schedule can make a huge difference to your fitness progress. I’m sure you’re familiar with the frustration of feeling like you’re starting from scratch, when your exercise and usual diet get disrupted for a week or more. The more you can reduce these setbacks, the quicker you reach your goals.

  • Testosterone: Some studies have shown that Vitamin D supplementation may increase testosterone levels in men. From a physical fitness perspective, this is beneficial as testosterone is one of the anabolic steroids – meaning that increased levels will support the gain of muscle mass as an adaptation to resistance training.

  • Fat loss/prevention of fat gain. Research has shown that low Vitamin D levels interfere with a hormone (Leptin) that regulates feelings of hunger. In other words, a lack of Vitamin D could cause you to over-eat as you will feel hungry, even after eating adequate calories. (Worth remembering here that low Vitamin D levels are a greater risk during winter, while exposure to sunlight is lower – and of course this also happens to be the time of year where you are more likely to indulge in extra treats, nights out, alcohol etc eg. around Christmas).

  • Regulates calcium & phosphate levels: Vitamin D is vital for healthy bones & teeth. Again, this is mainly a general health and wellbeing benefit. Deficiency can lead increase the probability of conditions such as rickets and bone pain (osteomalacia).

  • Possibly reduces the risk of some cancers: One large scale study in Japan* found that test subjects with ‘high Vitamin D levels’ were 22% less likely to get cancer than test subjects with ‘low Vitamin D levels’. However, increasing the dose of Vitamin D didn’t appear to produce a proportionate decrease in risk. In other words, once you reach a certain, (fairly moderate) level of Vitamin D, there was no additional benefit to taking more (at least from a cancer prevention perspective).*


Vitamin D can be sourced from food. Foods that contain Vitamin D include oily fish, red meat and eggs (egg yolks).


Tip: Vitamin D is a fat soluble vitamin. This means that it dissolves in, and is transported in fat. So if you are taking a Vitamin D supplement, take it with food (that contains fat). This way, you’ll make sure that your body is using the Vitamin D effectively rather than simply excreting it straight away.


The NHS recommends that adults “consider taking a daily supplement containing 10 micrograms of vitamin D”

In most cases, getting all of the nutrients that your body needs from whole foods is preferable. When it comes to vitamin D, this can be difficult. Even a diet rich in the above mentioned foods may not meet the RDI for Vitamin D.

The UK Department for Health recommends that you take a daily supplement containing 10 micrograms of vitamin D throughout the year if you:

  • aren't often outdoors – for example, if you're frail or housebound

  • are in an institution like a care home

  • usually wear clothes that cover up most of your skin when outdoors.

However, your body can produce it’s own Vitamin D when exposed to sufficient sunlight.

While this shouldn’t be a problem in the summer, getting enough sunlight exposure during winter may be a problem. This is why some people might choose to consciously eat more of the foods mentioned above, or take Vitamin D supplements.


In spring & summer, 20-30 minutes of sun exposure should be enough to allow your body the opportunity to produce your required Vitamin D. Try to make sure that you have plenty of skin exposed. Covering most of your body with clothing will block the sunlight getting to your skin. And obviously... make sure you don’t get sunburn!

The NHS also recommends that during autumn & winter, you should make a conscious effort to obtain your required intake from your diet, rather than relying on sunlight and to “consider taking a daily supplement containing 10 micrograms of vitamin D



As with most nutrients & supplements, there is such a thing as too much...

Excess Vitamin D can lead to liver, heart & bone damage. Follow the NHS/Department of Health guidelines. They are there for a reason. (10 micrograms per day during autumn & winter – NHS).

How Is It Possible That Vitamin D Comes From Both The Sun & Food?

The aim with both methods, is to get the inactive form of Vitamin D (as it exists in food and supplements) into your bloodstream and ultimately to your kidneys via the liver.

Once it arrive at the kidneys, Vitamin D is converted into its active form and then transported to many different areas of the body where it carries out it’s various processes, producing the benefits listed above.

Eating/supplementing Vitamin D means that it is transported into your bloodstream, directly from the gut...


UVB rays from the sun break down cholesterol close to the surface of your skin. The breakdown of this cholesterol releases Vitamin D3 (the exact same compound found in supplements) directly into your bloodstream.

From here, the process of converting inactive D3 into the active compound, is exactly the same as that which follows ingestion of Vitamin D3.

Providing that you are eating enough foods containing Vitamin D, or exposing yourself to the correct amount of sunlight, your body will enjoy the benefits of this essential nutrient.

Disclaimer: Speak to your GP if you believe you might be low/deficient in any vitamin/mineral (including Vitamin D) and/or if you are considering adding a Vitamin supplement to your diet.