SAD (or seasonal affective disorder) is a sub-form of major depression or bipolar, according to the Diagnostic and Statistical Manual of Mental Disorders, which most commonly occurs during the darker and colder autumn and winter months. Key identified risk factors include: a family history of the disorder, and living at northern latitudes. Specifically women, people with darker skin tones and individuals between the ages of 18 to 30 years of age are most at risk of developing the disorder. In order to have a diagnosis of SAD, the condition must be observed to improve outside of the colder seasons. Depending on the latitude, SAD has a prevalence of 1.9 – 9%. Individuals with lower levels of the metabolism regulating hormone adiponectin have also been observed to be at higher risk of developing SAD.

Nutrition and SAD

Vitamin D has been hypothesised to play a key role in SAD development due to reduced sunlight in northern latitudes during colder months. Additionally, it has been observed that there is a correlation between blood levels of Vitamin D and symptoms of depression, due to reduced levels of the neurotransmitters serotonin and dopamine. Vitamin D has also been hypothesised as being involved in circadian rhythm, which is affected by seasonal changes. However, supplementation of Vitamin D in SAD has yielded mixed results, and further studies are needed in this area.

Practical Interventions for Supporting Individuals with SAD

Due to the prevalence of Vitamin D in depressive conditions, the lack of sunlight during the winter months and the hypothesised role of Vitamin D deficiency in the development of SAD, increasing Vitamin D exposure is potentially of merit. This may be done through the following:

• Consuming foods which are natural sources of Vitamin D, such as oily fish including salmon and mackerel, egg yolks and organic milk and cheese
• Increasing exposure to sunlight in the winter months by being outside, particularly engaging in physical activities and spending time in nature 
• Supplementation of Vitamin D3. The RDA in the UK for Vitamin D is 10 micrograms (µg) or 400 IU. However, some individuals may benefit from supplementing higher levels of this vitamin, particularly if they have a higher BMI, a diagnosed mental health condition or darker skin pigmentation. Baseline levels of Vitamin D as established via blood test, calcium intake, genetics, oestrogen use, dietary fat content and composition, as well as co-existing diseases and medication use may also impact on Vitamin D requirements*.

*Note: before beginning any new supplement regimen, always consult your physician and a qualified nutrition practitioner.