Seasonal affective disorder or SAD is a type of depression that has a seasonal pattern. The symptoms often begin in the autumn as the days start getting shorter and are most severe during December to February, improving in spring. It’s estimated that SAD affects about two million people in the UK and is more common in women than in men, with up to three times more women than men affected. Current treatment is typically antidepressants and light box therapy.
What causes seasonal affected disorder?
The exact cause of SAD isn’t fully understood but it’s thought to be linked to reduced exposure to sunlight. It has been suggested that the lack of light affects the production of serotonin (a neurotransmitter that has been linked to depression and mood) and melatonin (a hormone that affects mood and sleep), and shifts the body’s circadian rhythm (our 24 hour internal clock), which may impact mood, hormones and sleep patterns, which may trigger depression.
A new review published in the journal Medical Hypothesis looks at the possible contribution of vitamin D to these mechanisms and hypothesises that a vitamin D deficiency may be behind them, and could have a regulative role in the development of SAD.
The review’s authors note that:
- Vitamin D levels in the body fluctuate with the changing seasons in response to available sunlight
- Past research has reported lower vitamin D levels in depressed patients compared to controls
- Vitamin D receptors are found in the hypothalamus, the region of the brain that encompasses the circadian timing centres
- Vitamin D levels have been suggested to affect serotonin levels
Vitamin D and depression
Past research does seem to suggest that there is a link between vitamin D and depression. However, we don’t know exactly what that link is. Research has not yet shown clearly whether low levels of vitamin D cause depression, or whether depression causes low levels of vitamin D. This means that we don’t know whether taking a vitamin D supplement, or getting more vitamin D by exposing your skin to sunlight or increasing dietary intake, will help to ease the symptoms of, or prevent depression.
What we do know though is that older people are advised to take a vitamin D supplement as they are at risk of vitamin D deficiency, particularly people who may not get much sun exposure like those living in care homes. Dietary sources of vitamin D include oily fish, eggs and fortified foods like powdered milk. Let’s try and ensure service users have adequate sun exposure and include vitamin D in their diet and supplements if appropriate.
