Guide To Vitamin D | Benefits, Sources & Deficiency Symptoms

Vitamin D, also known as the sunshine vitamin is in the news a lot these days.

In this article you can find:


What is Vitamin D?

Vitamin D is an essential vitamin for overall health, as well as strong and healthy bones. It has consistently been a hot topic due to the fantastic health benefits it can provide. It can be found naturally in small amounts in a selection of foods, including oily fish such as herring, sardines, tuna, and mackerel. To make this essential vitamin more available to the everyday consumer, foods such as juices, dairy products and cereals are often fortified with it.

Most vitamin D can be obtained through exposure to sunlight — in fact, you obtain around 80-90% [1] of it this way. When your skin gets exposed to the sun’s rays, it starts to produce vitamin D which is sent straight to the liver. Unfortunately, unless you’re living somewhere exotic, the chances are you’re missing out on this essential nutrient needed to boost your health levels. Not only that, but there are only optimal levels of vitamin D provided when there is an adequate amount of UV light of approximately a UV index of 3 or higher. This only occurs year-round near the equator.

Vitamin D is a vital factor in ensuring that your muscles and organs such as your heart, lungs, brain and liver work efficiently, [2] which is especially beneficial for athletes/individuals living an active, healthy lifestyle!


Vitamin D2 vs. D3

The term vitamin D actually refers to various different chemicals. The two most important forms relevant to human health and performance are the vitamins D2 and D3. These variations are essential for all individuals within the general population and athletes in particular, due to a number of reasons including its role in bone and muscle health as well as its effect on the immune system.

Vitamin D2 is predominantly synthesized by plants and can be consumed through the diet and in supplements, whereas vitamin D3 can actually be synthesised in the human body upon exposure to the sun.

According to some studies, vitamin D3 is the form in which the majority of people are deficient. To combat this, it is available in supplements and in a range of fortified foods (e.g. spreads and cereal products). Foods in which this essential vitamin occurs naturally include egg yolks, milk, and fatty fish.

Despite its availability, many people in the UK are still vitamin D deficient, especially during the winter months in which ethnic minorities, pregnant women and children are particularly at risk. As a result, vitamin D supplementation is widely advised.


Benefits of Vitamin D

1. Vitamin D for Weight Loss

In a study by Major et al (2007), the consumption of calcium and vitamin D was analysed during a weight-loss intervention. In this study, 63 individuals were assigned to consume a supplement or placebo over 15 weeks. After 15 weeks, it was found that the calcium and vitamin D supplementation caused a decrease in LDL cholesterol and waist circumference. Overall, the combination enhanced the beneficial effect of reducing the lipid and lipoprotein profile in overweight or obese women with usual low daily calcium intake.

2. Bone Mineralisation & Joint Pain

Vitamin D helps to maintain bone mineralisation by ensuring there is a plentiful supply of calcium in the bloodstream. This is achieved by enhancing the absorption of dietary calcium from the large and small intestines. Studies have also observed a positive effect on the deposition of calcium in bone [3].

Those who train with resistance work will find that they can have aches and pains in the joints, which is perfectly normal. When you’re looking to achieve optimal health there may be some niggles and pains along the way. Vitamin D3 can help prevent and treat any longer term issues with weak bones and bone pain. This can further enhance your physique by allowing you to continue working out into old age.



Vitamin D Side Effects

Vitamin D is generally safe when taken in the correct amounts. Most people don’t experience side effects unless they take too much. Taking too much can occasionally induce feelings of weakness, fatigue and a dry mouth/metallic taste[1].


Vitamin D Deficiency Signs & Symptoms

Signs and clinical symptoms of vitamin D deficiency include weak bones and muscles, and has even been associated with asthma in children.

It is crucial to receive an adequate intake of vitamin D in order to maintain a healthy immune system and muscle function which makes it an essential part of every athlete’s diet.

There are several signs and symptoms of vitamin D deficiency which you should look out for. Just because you have some of these symptoms doesn’t necessarily mean you are deficient, however it is always best to consult your doctor to be on the safe side!

1. You feel down

Serotonin, the hormone which controls your mood, rises when exposed to bright light and falls with decreased exposure. Scientists have concluded that feeling down may be a symptom of being vitamin D deficient, since you may not get enough natural sunlight [5].

2. Your bones ache

According to Dr. Holick, many patients with aching bones are misdiagnosed by their doctors.

“Many of these symptoms are classic signs of vitamin D deficiency osteomalacia, which is different from the vitamin D deficiency that causes osteoporosis in adults,” he says. “What’s happening is that the vitamin D deficiency causes a defect in putting calcium into the collagen matrix into your skeleton. As a result, you have throbbing, aching bone pain.”

3. You are obese or overweight

Since vitamin D is fat soluble, body fat can ‘collect it’. The more body fat you have the more of the vitamin is absorbed meaning less can be properly utilised. The same can be said for people with large amounts of muscle mass or those with a larger frame. The larger you are, the more vitamin D you require.

4. Head sweating

According to Dr. Holick, head sweating may be one of the first symptoms of vitamin D deficiency [6]. It can be common in new-born babies.



Who should take Vitamin D?

Vitamin D deficiency can occur across the population spectrum and is not limited to children, ethnic minorities or elderly people. Studies have shown it is difficult to find populations not deficient in vitamin D, especially those where sunshine is not in abundance such as the U.K and Ireland.

Those with a darker skin tone, however, may be at greater risk of deficiency as they need more sun exposure in order to produce the same amount of the vitamin as someone with lighter skin.

Although both D2 and D3 variants are available in supplemental form, D3 is the most clinically recommended form to take. As an essential vitamin that isn’t largely synthesised in the body, it is likely that most people would benefit from supplementation.

Vitamin D Sources and Dosage


If you obtain vitamin D naturally from food or in supplement form, it is sent to the liver by the gut where it is changed into a substance known as 25(OH)D[2]. This can be used all over your body and is turned into the activated form.

Vitamin D can be taken in supplement form in numerous ways. It’s available over the counter as a stand-alone vitamin, in combination with calcium, or is often included in a broad spectrum multivitamin. As previously mentioned, vitamin D3 is the version of this vitamin recommended in clinical practice to obtain the maximum benefits from supplementation.

Sunlight is the biggest source of vitamin D, however the best source is from oily fish such as herring, sardines, tuna and salmon. Other dietary sources include fortified foods such as cereals, milk and other dairy produce.

These foods do contain moderate amounts of the vitamin however if you are deficient, then the most convenient and cheapest way is to invest in a supplement. There are a few different kinds of supplements available. One is vitamin tablets, such as Vitamin D3. These are a great direct source and are easy to consume so you can instantly hit your daily goals!

Another great option is cod liver oil which has the added benefit of sourcing some of your daily vitamin A and essential fatty acids. These, too, are easy to take and are very popular.

Finally, you can opt to take a multivitamin. These do not contain as much vitamin D as the others so are best for those who do not need to increase their daily intake by as much, and those who would like to reap the benefits of other minerals (e.g. magnesium, calcium, zinc, selenium) and vitamins (e.g. A, E, B, K, and C).


Vitamin D Sources Examples

  • Get More Sun/ UV lamps
  • Fatty Fish — 3 ounces of salmon contains around 450 IU
  • Canned Tuna — 150 IUs per 4 ounces
  • Egg Yolks — 40 IU
  • Mushrooms — Portobello mushrooms 400 IU per 3 ounces
  • Fortified Milk
  • Fortified cereal
  • Cod Liver Oil — 1300 IU
  • Supplements


 Vitamin D Dosage

Studies have shown that 2500 IU is an effective daily dosage of vitamin D without causing any adverse effects on participants whilst retaining all the benefits of this crucial vitamin. Numerous studies have also suggested that the current guidelines need to be reviewed to increase the minimum recommended dosage to a more effective level than is currently suggested in government guidelines.

It’s important to know the dosage of vitamin D before you go about adjusting your intake. Updated last in 2010, the US Institutes of Medicine (IOM) have currently set the dosage at:

  • Infants 0-12 months – 400 IU (10 mcg)
  • Children 1-18 years – 600 IU (15 mcg)
  • Adults to age 70 – 600 IU (15 mcg)
  • Adults over 70 – 800 IU (20 mcg)
  • Pregnant or lactating women – 600 IU (15 mcg)


Take Home Message

Vitamin D is a really essential vitamin for everyone to ensure the health of your immune system, bones, and vital organs. There are lots of sources, however it’s best advised to take it as a supplement if you find that you’re deficient.

It’s hard to overdose if you follow the dosage information on your supplement or prescription.

Remember, if you believe you may be vitamin D deficient, it’s always best to consult your doctor rather than self-diagnose.

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Our articles should be used for informational and educational purposes only and are not intended to be taken as medical advice. If you’re concerned, consult a health professional before taking dietary supplements or introducing any major changes to your diet.

[1] WebMD Vitamin D fact file – accessed on 7th August 2015


[2] Vitamin D Council – accessed on 7th August 2015


[3] Manual of Nutrition – Tenth Addition, Reference Book 342, pages 63/64 – accessed on 7th August 2015


[4] Vitamin D’s Role in health – deterministic or indeterminate? – Stephanie Dunne and Jenna A. Bell, PhD, RD, Today’s Dietitian, Vol. 16 No. 7 P. 48 – accessed on 7th August 2015


[5] American Journal of Geriatric Psychiatry – Vitamin D Deficiency Is Associated With Low Mood and Worse Cognitive Performance in Older Adults – accessed on 7th August 2015


[6] Vitamin D for Health: A Global Perspective – accessed on 7th August 2015

[7] Vitamin D: Health Benefits and Recommended Intake – accessed on 7th August 2015

[8] Zittermann, A., Frisch, S., Berthold, H. K., Götting, C., Kuhn, J., Kleesiek, K., … & Koerfer, R. (2009). Vitamin D supplementation enhances the beneficial effects of weight loss on cardiovascular disease risk markers. The American journal of clinical nutrition89(5), 1321-1327.

[9] Major, G. C., Alarie, F., Doré, J., Phouttama, S., & Tremblay, A. (2007). Supplementation with calcium+ vitamin D enhances the beneficial effect of weight loss on plasma lipid and lipoprotein concentrations. The American journal of clinical nutrition85(1), 54-59.

[10] Larson-Meyer, D. E., & Willis, K. S. (2010). Vitamin D and athletes. Current sports medicine reports9(4), 220-226.

[11] Mathieu, C., Gysemans, C., Giulietti, A., & Bouillon, R. (2005). Vitamin D and diabetes. Diabetologia48(7), 1247-1257.



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