Depression and Seasonal
Affective Disorder 

Vitamin D3 deficiency has been linked to an increased risk of serious health problems and mood disorders including Depression and Seasonal Affective Disorder (SAD).

In the past few years, maintaining high levels of vitamin D sufficiency has emerged as one of the most important preventive factors in human health and wellbeing. It is now widely recognised as an independent risk factor for numerous health problems. Research has found that Seasonal Affective Disorder tends to be prevalent when vitamin D stores are typically low. ⁽¹⁾ Current statistics indicate that 87% of Britons are deficient in vitamin D during the winter months, therefore, increasing the proportion of individuals who may be predisposed to suffering from mood disorders including winter SAD.

Vitamin D3 is known as the "sunshine vitamin" because the body produces it naturally when exposed to the sun's ultra violet rays; 90% of vitamin D3 is produced from the sun and only 10% is obtained from the diet, making sun exposure essential in order to produce sufficient vitamin D3 levels. ⁽²⁾ However, factors such as busy working lifestyles and increased awareness of skin cancer and use of high factor sun lotions means that more people are not getting the required amount of sunshine to produce sufficiently high levels of vitamin D3 in the body. In the UK, very little vitamin D is synthesized in the skin during sun exposure between October and March because of the sun's angle and strength. This explains the seasonal variation in vitamin D levels between summer and winter and contributes significantly to the large proportion of Britons who are deficient in this essential vitamin.

Phototherapy, commonly known as light therapy is widely used in the treatment of patients suffering from winter SAD, and is shown to be relatively effective. ⁽⁶⁾ It has been suggested that this treatment is effective due to the ability of high level intensity lights to synthesize vitamin D in the skin. Research has been carried out to test the efficacy of vitamin D supplementation on mood disorders including winter SAD and depression; results indicate that vitamin D concentrations in the blood do have an effect on mood disorders and intensity of symptoms. ^{(1) (4) (5)}

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