Vitamin D and Fatigue

Feeling tired?  Consider checking your vitamin D status

Fatigue is a very common complaint, characterized by lack of energy, feelings of tiredness that are not relieved by sleep, and an inability to function mentally or physically. Fatigue may result from a number of different aetiologies including lack of sleep, anxiety, anaemias, underactive thyroid, adrenal hypofunction, etc.

Vitamin D deficiency and fatigue

Vitamin D deficiency is a less well-known contributing factor to fatigue.

While researchers are still trying to determine the mechanisms by which vitamin D deficiency contributes to fatigue, they all agree that vitamin D supplementation in deficient individuals, improves fatigue.

Some studies suggest that Vitamin D deficiency affects mitochondrial energy production; (mitochondria are organelles found in abundance in skeletal muscles and liver cells and are considered the ‘power house’ of the cell). Therefore, mitochondrial dysfunction will impair energy production, contributing to fatigue.

Sun exposure and vitamin D  

Some studies found that higher levels of sun exposure were associated with reduced levels of fatigue (vitamin D may be one of the reasons why we feel so much better on a sunny day).

Vitamin D deficiency is prevalent in the UK as we can only make vitamin D via sunlight, between March and October (UVB is the primary source of vitamin D for most individuals).

Research shows that at least 80% of human vitamin D has to be synthesized in the skin by the action of UVB radiation, the portion of sunlight that stimulates our skin to produce vitamin D.  However, the timing of UVB sunlight exposure is important; between 10 am – 2 pm is ideal time for UVB exposure, while after 2pm skin damaging UVA rays increase.  It is therefore recommended that 5 – 30 minutes of sunlight exposure at least twice a week, between 10 am – 2 pm is the most effective for vitamin D synthesis (providing your liver and kidneys are healthy, as vitamin D is further metabolized in these organs).

In the summer, 30 minutes of full body exposure to sunlight by fair-skinned people (without a sunscreen) can produce 20,000 iu of vitamin D (in dark skin people melanin blocks UVB rays, and those individuals require at least 3 – 5 x longer sun exposure to make the same amount of vitamin D)

Unfortunately, UVB ray also play a key role in the development of skin cancer, hence most of us use sun screen protection, which also prevents adequate vitamin D synthesis

Can we get vitamin D from the diet?

At most, we get 10% of our vitamin D from food.  Vitamin D3 (the active form of vitamin D) is naturally present in oily fish (such as salmon, mackerel & sardines), cod liver oil, eggs, liver, also in milk, margarine & fortified foods such as breakfast cereals.  

For example, 100g of wild salmon contain 500-1000 iu of vitamin D, while a 100g of farmed salmon contains only 100 – 250 iu of vitamin D.

How to test your vitamin D?

Your GP will test your serum levels of vitamin D, particularly if you are experiencing any health issues

You can also visit a CNHC-registered Nutritional Therapy Practitioner who will organise a test for you, interpret it and give you nutritional recommendations accordingly.


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