Vitamin D: The Most Important Vitamin?

Updated: Jan 28

I seem to be on a vitamin D binge recently. This could be because we are finally in the ‘two months of London sunshine’ that we get every year. Or it could be because this article covers the complex and lengthy topic of vitamin D which I mentioned briefly in 'The Benefits of Being Outdoors'. Maybe it’s a combination of the two. I digress. Anyway, let’s begin with what exactly vitamin D is:

Vitamin D is the name given to a group of fat soluble secosteroids - a type of steroid with a broken ring - which are responsible for biological processes such as calcium, magnesium and phosphate absorption, immune function and even anti-inflammatory promotion. (1) There are many different types of vitamin D, but the most important ones for human health are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Of the two, D3 increases vitamin D levels in the body most effectively. (2)

Directly exposing larger muscle groups to natural sunlight in spring and summer afternoons can result in vitamin D being synthesised by the body. One half-an-hour full body tanning period in strong sunlight triggers a chemical reaction with cholesterol to produce a weeks worth of vitamin D, approximately 10,000 - 20,000IUs, in the skin. (3) In fact, studies suggest that exposure at midday is actually better for you. (4)(5) Access to sunlight in autumn and winter months will not increase vitamin D levels much, if at all; neither will early morning or late evening sun exposure. (6) It is, therefore, recommended to eat foods high in vitamin D or supplement with vitamin D3 during these periods, sunbathe closer to midday, or travel to countries with warmer climates when your home country becomes colder and darker. Intend to expose your legs, back, and chest to natural sunlight without burning. It is sensible to avoid using sunscreen for the first 5-10 minutes after which (depending on skin colour, location, diet, and time of day) one should move into shaded areas or apply a healthy sunscreen if your skin is still in the sun, as tanning and burning are signs of damaged skin which can dramatically increase the risk of skin cancer.

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Sources Of Vitamin D

A diet high in animal protein and saturated fat has the potential to improve resistance to sunburn and reduce the risk of poor health from D3 deficiency even when supplementation and sun exposure are avoided (7).

The following foods contain vitamin D which may prove useful to bolster health in periods where exposure to sunlight - the bodies main source of vitamin D - is reduced, and when the sun's rays become weaker in colder months. Bear in mind, dietary vitamin D was an unreliable source before supplements were made.

Fatty Fish - fish with a high fat content such as mackerel and sockeye salmon are high in vitamin D. Make sure your fish is caught in the wild and not farmed, as farmed fish contain considerably lower levels of vitamin D. Cod liver oil can also be consumed in small doses (approximately 1/2-1 teaspoon daily) because it contains many healthy vitamins, however, one should prioritise fish oil for its potent omega-3, DHA/EPA content.

Egg Yolk - egg yolks from pastured hens contain good levels of vitamin D. Again, it is important your eggs are from free range, organic or pastured chickens as these have a higher vitamin D content.

Mushrooms - mushrooms, especially Shiitake mushrooms, synthesise vitamin D from sunlight much like humans, however it is converted to vitamin D2 and not vitamin D3. Include mushrooms in your diet, but do not rely on them for vitamin D3.

Supplements - vitamin D supplementation may be a good idea if you have been diagnosed with low levels, however it is always best to obtain your vitamin D from natural sources. For those who originate and live in the Northern Hemisphere, supplementation should be consistent at around 2,000IU a day all year round (8). A study found that supplementation of up to 10,000iu per day is safe, and potentially favourable in individuals who do not have conditions that predispose them to high blood calcium (such as hyperparathyroidism and acidosis).


The following foods should be avoided in order to prevent nutritional deficiencies and over-conversion of the vitamin:

Fortified Or Processed Foods - they increase vitamin D requirements because the body uses available vitamin D for calcium regulation. These foods commonly contain vegetable oil, sugar and grains among other harmful ingredients, which also decrease calcium absorption. Additionally, health problems can arise and become worse through nutritional deficiencies which these foods could be contributing to.

Dangers Of Too Much Vitamin D

Even though it is one of the most important vitamins for the human body, there are dangers linked to supplemental overconsumption. Toxic doses, which lead to Hypervitaminosis D, typically occur at or above 40,000 IU, but can occur as low as 10,000 IU. Single, extremely high supplemental doses lead to toxicity, not natural exposure to sunlight (9).

One of the functions of vitamin D is to regulate levels of phosphate and calcium in the intestine for optimal bone growth and mineralisation. Dangerously high calcium levels in the body can lead to hypercalcuria (also known as kidney stones). In addition, those with hyperparathyroidism over-convert the vitamin. Both can be easily avoided with regular (or even irregular) check-ups to ensure you are not over-converting vitamin D.

What Causes Vitamin D Deficiency?

As most of our vitamin D intake comes from sun exposure, the main cause of vitamin D deficiency is due to the metabolic pathway leading to the synthesis of vitamin D from UVB rays. Several factors affect this such as:

Lack Of Sunlight

If you live in a country further from the equator where there is generally less sunlight, then you are at a higher risk of being vitamin D deficient. Lifestyle factors also affect this such as working indoors. Experts recommend 10-15 minutes of direct sun exposure per day for individuals with a light-to-medium skin colour for sufficient vitamin D absorption. Those with darker skin (we will get to that in a second) and those living further away from the equator may need to spend more time in the sun (10).

Skin Tone

Skin tone is determined by the amount of melanin present in the skin. The more melanin, the darker the skin. Melanin is the body's mechanism of protection against UVA and UVB rays (both of which are very damaging in excessive quantities) and higher levels of melanin reduces the amount of UVA and UVB rays which penetrate the skin. This means that those with a higher amount of melanin in their skin have a reduced capability to synthesise vitamin D due to the lowered levels of UVB light exposure.


Aside from the dangerous chemicals present in most sunscreens which can lead to physiological and even environmental harm, sunscreen use can reduce the amount of vitamin D obtained from the sun. By blocking UVB rays from being absorbed, it essentially leads to the shut down of vitamin D synthesis. Choose mineral sunscreen containing zinc oxide, without parabens or retinyl palmitate (11); this will further protect you from both UVA and UVB rays.

How Do I Know If I Am Vitamin D Deficient?

With the ever-increasing shift away from spending time outside associated with modern life and work, the chances of people developing a vitamin D deficiency increases. If you have dark skin and are conscious of not spending enough time exposed to sunlight then it may be worth speaking to your doctor or physician for testing if you experience some of these symptoms:

Reduced Immune Function - if you find you are constantly battling a flu or other infection then it could be a sign you are deficient in vitamin D. One of vitamin D’s functions is to support the body's immune system (12). Studies of people suffering from chronic lung disorders showed that supplementing with vitamin D provided significant benefits after a year.

Bone And/Or Back Pain - as vitamin D is responsible for calcium absorption, it seems obvious that a deficiency would manifest itself as bone pain. Studies have shown a link between low vitamin D levels and back pain, and in one controlled study, it was shown that people with a vitamin D deficiency were twice as likely to experience pain in their legs, ribs and joints.

Osteomalacia & Osteoporosis - as mentioned previously, vitamin D deficiency impairs bone mineralisation and can lead to osteomalacia (gradual softening of the bones) and osteoporosis (increased bone weakness).

Muscle Pain/Weakness - vitamin D plays a role in neuromuscular function and can impact protein synthesis. Studies have shown that people deficient in vitamin D experience decreased strength and increased muscular atrophy.


Vitamin D deficiency is an increasing problem in many countries and can lead to serious illness if left unaddressed (13). Fortunately, assuming there is no specific medical condition leading to the deficiency, it is easy to redress the imbalance. Aim to spend enough time in the sunlight without burning where possible, and fortify your diet with vitamin D rich foods such as fatty fish, pastured eggs and mushrooms. Only consider supplementation if you are at high risk of developing a deficiency and always speak to your doctor before taking any supplement.

Related post: What Should We Be Eating?

Related post: How Collagen Transforms Health

Related post: Spend More Time Outdoors


John Maitland

John Maitland is the co-founder of 'The Evolved Way.’ A personal trainer with over 10 years’ experience, he has worked alongside a wide range of leading CEOs, entrepreneurs and medical professionals. John is a keen athlete and holds a black belt in Shaolin Kung fu. A fan of the great outdoors, he can often be found exploring the British countryside and mountains...or breaking pine boards with his fingers.

Samson Hodin

Co-founder of 'The Evolved Way', and experienced personal trainer, Samson practices what he preaches. His own healthy lifestyle, which informs this site, is based on understanding the right way to eat and exercise, not excluding of course going out and enjoying life knowing you can still feel and look good.

#Vitamins #Outdoors #Lifestyle



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