Vitamin D is one of the most important vitamins that our body needs to function optimally.

POSTED 1 year ago

Why is Vitamin D so important to you through the Winter?

Source:  Education Administrator, Biocare

Vitamin D is one of the most important vitamins particularly for your immune system to function optimally. Vitamin D is best-known for its bone supporting function whereby it plays an important role in enhancing the absorption of calcium and phosphorus. Other important roles of vitamin D include regulating our insulin production for optimum blood sugar balance, enhancing immunity, supporting cardiovascular health and regulating our mood. Despite its importance, vitamin D deficiency is unfortunately very common, particularly within the UK population. This is mainly due to our lack of sunlight exposure (which is our main source of vitamin D) along with a low intake through the diet. Other factors which further contribute towards low vitamin D levels include old age, pregnancy and breastfeeding, dark or covered skin, sunscreen use, obesity and the intake of certain medications such as metformin.


As we are just coming out of Winter where our exposure to sunlight was very limited, it is important to ensure that our vitamin D levels are kept within optimum levels. This is particularly important as vitamin D can enhance our immune response against various infections which are more common during winter such as tuberculosis, influenza and viral upper respiratory tract infections.[1] It is also supportive of mental health conditions such as Seasonal Affective Disorders (SAD) and depression, whereby vitamin D supplementation portrayed effectiveness in reducing depressive symptoms in SAD patients.[2] It is suggested that vitamin D may enhance serotonin production hence its mood-enhancing effects.[3] Due to the Western diet and an indoor lifestyle, it is becoming harder for us to maintain adequate levels of vitamin D in our body. Food sources of vitamin D include oily fish, such as salmon, mackerel and sardines, eggs and raw milk. However, due to the increase of fish and poultry farming, vitamin D levels in these sources are lower than expected. For example, farmed salmon was found to have approximately 75% less vitamin D in comparison to wild salmon.[4] Therefore, a vitamin D supplement is essentially the best way of ensuring that we get our daily dose of vitamin D.


The UK Department of Health have always recommended adults over 65 years, pregnant and breastfeeding women, babies and children to supplement with 10 micrograms (400 IU) of vitamin D, especially if the infant is breastfed or if receiving less than 500ml of suitably fortified formula milk. However, more recent recommendations (2016) have advised that everyone in the UK should supplement with vitamin D during autumn and winter, and all year round for those with limited sunlight exposure even during summer such as those who cover up for religious reasons or individuals with an indoor, sedentary lifestyle e.g. working in an office. Where there is a deficiency, individuals will require significantly larger doses of vitamin D of around 2000-4000 IU administered for at least 3 months and levels then retested. Obese individuals, patients with malabsorption syndromes, and patients on glucocorticoids, anti-seizure and AIDS medications may require higher doses of vitamin D (up to 2-3 times higher – at least 6000–10 000 IU/day). We recommend that you get your serum vitamin D levels tested before taking high doses of vitamin D. A vitamin D test can often be requested from your GP.

Vitamin D is a fat soluble vitamin, so individuals with compromised digestion or difficulty digesting fat may not be able to absorb and metabolise vitamin D well. It is important for these individuals to select an emulsified (pre-digested) version of vitamin D to ensure optimal absorption.

We strongly recommend that you include vitamin D as part of your winter supplement protocol this year.


[1] Yamshchikov, A.V., Desai, N.S., Blumberg, H.M., Ziegler, T.R. and Tangpricha, V. (2009) Vitamin D for treatment and

prevention of infectious diseases: a systematic review of randomized controlled trials. Endocrine Practice, 15 (5), 438–449.

[2] Gloth, F.M., Alam, W. and Hollis, B. (1999) Vitamin D vs broad spectrum phototherapy in the treatment of seasonal

affective disorder. Journal of Nutrition, Health and Aging, 3 (1), 5-7.

[3] Landsdowne, A.T.G. and Provost, S.C. (1998) Vitamin D3 enhances mood in healthy subjects during winter.

Psychopharmacology, 135 (4), 319- 323.

[4] Lu et al. (2007) An evaluation of the vitamin D3 content in fish: is the vitamin D content adequate to satisfy the dietary requirement for vitamin D. Journal of Steroid Biochemistry and Molecular Biology. 103 (3-5): 642-644.