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Can vitamin D help the winter blues?


As the summer draws to a close and schools start again, some get sad. As the days shorten, others get seasonal affective disorder, or Sad.

Sad is a form of winter depression with varying symptoms, including sleep problems, fatigue, overeating, irritability, anxiety and loss of libido. These can range in seriousness from mild (the winter blues) to seriously debilitating. Sad is distinguished by the way the symptoms develop between September and November, and disappear in March or April.

A diagnosis is made when this pattern recurs during three consecutive winters. Around 5 per cent of people living in northern latitudes are thought to have the more serious form of Sad. A recent survey found about 20 per cent of people living in Ireland experience Sad to some degree.

Professional help should be sought when the Sad symptoms are more serious. In less serious cases, getting outdoors more often can help, or using “light therapy” with special light bulbs. Much interest has developed in vitamin D supplements for Sad, because its levels in the body are also dependent on sunlight.

Vitamin D is best known for its role in calcium metabolism and maintaining healthy bones. However, it is involved in many other functions in the body, including the brain. We make our own vitamin D when sunlight hits the skin and triggers a chemical reaction. About five to 15 minutes of direct sunshine can produce enough vitamin D for the day. Since that doesn’t happen every day in Ireland, vitamin D is also available in the diet. Fatty fish are one of the few natural dietary sources, which has led to milk and other foods being fortified with vitamin D. Vitamin D supplements are also available.


Much of the information on vitamin D and Sad comes from epidemiological studies. These are large surveys, also called population studies, that collect information on various lifestyle factors and health. After statistical analyses, they produce “correlations” that connect various items in the survey. Such connections are important to direct further research, but do not show if one item caused the other.

Early population studies found relatively high incidences of Sad in Scandinavia. Unexpectedly, the incidence in Iceland was very low. Genetic factors were suggested as a cause, but fish consumption is very high in Iceland. It has been suggested that the fish provide sufficient vitamin D to ward off the winter blues.

However, other population studies have produced contradictory results. For example, a 2008 study found significant correlations between serum vitamin D levels and both the risk of depression and its severity in more than 1,000 Dutch people older than 65. In July 2010, another study found no significant correlations between vitamin D levels and depression in almost 4,000 US adults. So overall, the results are confusing.

Regardless, randomised controlled trials are needed to show whether vitamin D can prevent or treat Sad. One such trial involved more than 400 men and women who received either high-dose vitamin D, low-dose vitamin D or a placebo. They found that those taking vitamin D for a year had less depression, and that the higher dose produced better results.

With Sad patients, three smaller studies showed beneficial results for those randomised to vitamin D, while three other studies showed no differences with the placebo group. Daily doses in these studies ranged from 400 IU to almost 6,000 IU, making it difficult to compare their results directly.


Vitamin D is safe when taken up to the recommended upper limit of 2,000 IU per day. Much higher doses have not caused adverse effects when taken for short intervals. Taking higher doses, especially long-term, can lead to excess calcium in the body, which causes muscle weakness, fatigue, headache, nausea and more serious kidney problems.


At this point, a growing body of evidence shows that vitamin D is connected to mood levels. However, the evidence that vitamin D supplements prevent or relieve Sad is inconsistent. Beneficial effects have been found, especially for women and older people. Given that vitamin D is safe and inexpensive, and has many health benefits, those with Sad symptoms could benefit from a trial period. The usual recommendation is 1,000-2,000 IU vitamin D per day from September to March. Getting outdoors is also helpful.

Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University. He authored Alternative Medicine: The Christian Handbook, Updated and Expanded Edition, Zondervan, 2007