Seasonal Affective Disorder (SAD)

SAD is a mood disorder featuring depressive symptoms and occurs during winter when there is less daylight. The decrease in sunshine coincides with a drop in vitamin D which may affect serotonin (happy hormone) levels in the brain. When absorbed by the sun or consumed via food, vitamin D is transported to the liver and kidneys where it is converted to its active hormone. Every tissue in the body has vitamin D receptors, including the brain, heart, muscles, and immune system, meaning that vitamin D is needed for the body to function.

With this in mind, it’s essential that we optimise vitamin D levels. Although not as effective as in the summer months, you can still head out for walks in the winter to help top up vitamin D. Research shows that midday is the best time to do this (Rhodes et al. 2010). Food sources of vitamin D include mushrooms, tofu eggs, dairy products, and oily fish such as salmon and anchovies.

People more at risk of low vitamin D levels are those with indoor lifestyles including those who work from home. Other things that may contribute are pregnancy and breastfeeding, old age, dark or covered skin, obesity and low magnesium status.

As much as 25% of the UK population may be deficient in vitamin D but fortunately, we can take control of this by supplementing. Evidence shows a link between low vitamin D and mental illness showing that optimising vitamin D levels may work towards improving psychological well-being. A recent study has indicated that supplementation can even reduce the risk of having a respiratory infection (Martineau et al. 2019).

What Else Can Help with SAD?

Approaches to aid symptoms of SAD are centred around replacing the lack of sunshine using light therapy (Bright Light therapy (BLT) or phototherapy) in the morning. Light therapy should not be used in conjunction with medications such as lithium, melatonin, phenothiazine antipsychotics, and certain antibiotics. Therapeutic solutions such as CBT have also been shown to help. All solutions that aim to tackle SAD symptoms are unique to each individual – there is no one size fits all approach so make sure you are getting the right advice from the right people.


Martineau, A.R., Jolliffe, D.A., Greenberg, L., Aloia, J.F., Bergman, P., Dubnov-Raz, G., Esposito, S., Ganmaa, D., Ginde, A.A., Goodall, E.C. and Grant, C.C., 2019. Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. Health Technology Assessment, 23(2), pp.1-44.

Rhodes, L.E., Webb, A.R., Fraser, H.I., Kift, R., Durkin, M.T., Allan, D., O’brien, S.J., Vail, A. and Berry, J.L., 2010. Recommended summer sunlight exposure levels can produce sufficient (≥ 20 ng ml− 1)