How vitamin D deficiency in winter poses hazards for our health (and what to do about it)

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The contracted days and climatic changes that come at this time of year can us not only cold, but short on sunlight too. Getting adequate exposure to the sun’s rays is important for maintaining mood, and it’s action on the skin is also the main way the body meets its needs for vitamin D ” a nutrient which research has shown to have a range of benefits for the body and brain. Studies show that the winter months can leave us low in vitamin D. So, what are the consequences of vitamin D deficiency, and what can we do to ensure we remain topped up with this important nutrient throughout the winter?

Vitamin D is perhaps best known for its role in the manufacture of healthy bone. However, evidence that has been amassing over the last few years has found that vitamin D has the ability to reduce the risk of the development and spread of cancerous tumours. No surprise then that studies show that increased sunlight exposure is associated with a decreased risk of several forms of cancer, including those of the breast, prostate and colon.

What is perhaps even less well known is that vitamin D seems to have an influence on the wellbeing of not just the body, but the brain also. Published research shows that this nutrient actually has the potential to combat seasonal affective disorder (SAD) “sometimes referred to as the ‘winter blues’ or ‘winter depression’. In one study, just five days of treatment with vitamin D (at a dose of 400 or 800 IU per day) was found to improve winter mood [1]. Further evidence for the potential for vitamin D to alleviate SAD came from research in which individuals were treated with either 600 or 4000 IU of vitamin D each day for at least six months. Both dosages of vitamin D led to improvements in the participants’ mood and general well-being, with those on the higher dose of vitamin D benefiting the most [2]. This link between vitamin D and mood helps to explain, at least in part, the biochemical basis for SAD.

Bearing in mind its importance for mental and physical health and wellbeing, it makes sense to ensure that our bodies get enough vitamin D throughout the winter months. Seeing as most of our needs for this nutrient generally come from the action of sunlight on our skin, then it helps for us to get out more. This is an issue in the winter, of course, as we are less likely to venture out when the weather is inclement. Wrapping up to protect ourselves from the elements and the shortened days obviously compound the problem. So, whenever possible, it helps to get out more, particularly on bright days. Taking a walk for half and hour or more at lunchtime, for instance, can do much to stimulate vitamin D production in the body.

Apart from sunlight, the other major source of vitamin D is our diet. ‘Oily’ fish such as salmon, mackerel and sardine are rich in vitamin D, and including at least 2 or 3 portions of these in the diet each week will help. Another option for those looking for a convenient food course of vitamin D is cod liver oil ” which contains up to about 500 international units (IUs) of vitamin D per teaspoon. Please check the labels as the vitamin D level in cod liver oil is highly variable from brand to brand.

Cod liver oil, like other fish oils, is also rich in so-called omega-3 fats. These come in two main forms: docosohexaenoic acid (DHA) and eicosapentaenoic acid (EPA). A high consumption of these fats has been linked with a reduced risk of ‘cardiovascular’ conditions such as heart attack and stroke. Omega-3 fats have a natural anti-inflammatory effect in the body, and there is some thought that this biochemical benefit may be part of the explanation for why cod liver oil can provide relief from conditions like osteoarthritis and rheumatoid arthritis. And like vitamin D, these fats also have benefits for the brain. DHA appears to be important for the structural integrity of the brain, while EPA seems to have a more important role in the day-to-day running of the brain. Omega-3 fats show promise in the prevention and/or treatment of many mental ailments including depression and dementia [3].

To get useful levels of vitamin D and omega-3 fats from cod liver oil one needs to take in the region of 1 ” 2 teaspoons (5 – 10 mls) a day throughout the winter. It is generally uneconomical to do that with capsules containing, say, half or one ml of cod liver oil. For this reason, the most cost effective approach is to take cod liver oil off the spoon. One obvious barrier to this is taste. Fortunately, cod liver oils that have been naturally flavoured (often with lemon or orange) are now available and represent a practical option for those who simply don’t like the taste of cod liver oil and may even have positive aversion to it as a result of being force-fed it in childhood. Because of its rich stash of vitamin D and other nutrients, cod liver oil is one supplement well worth considering for individuals keen to preserve their physical and mental wellbeing throughout the winter months.


Cod liver oil also contains vitamin A ” which has been linked with an increased risk of birth defects. Pregnant women or women who may become pregnant are advised not to consume more than 10,000 IU of vitamin A per day in supplement form. This equates to about 2 teaspoons of cod liver oil per day.


1. Lansdowne AT, et al Vitamin D3 enhances mood in healthy subjects during winter.
Psychopharmacology (Berl). 1998;135(4):319-23.

2. Vieth R, et al. Randomized comparison of the effects of the vitamin D3 adequate intake versus 100 mcg (4000 IU) per day on biochemical responses and the wellbeing of patients. Nutrition Journal 2004;3:8 []

3. Schaefer EJ , et al. Plasma Phosphatidylcholine Docosahexaenoic Acid Content and Risk of Dementia and Alzheimer Disease: The Framingham Heart Study
Archives of Neuroogy. 2006;63:1545-1550

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