Here is a link to a very good article on why we need vitamin D and how it’s low levels in the body can contribute to various health issues, including mental health problems.
Our psychological wellbeing is directly related to our physical state. Quite often depression appears to be a result of vitamins or minerals deficiencies. One of the important elements, which could influence our mental state, is the vitamin D.
There are many causes of depression. Researchers are now discovering that vitamin D may play an important role in our mental health. Vitamin D acts on the areas of your brain that are linked to depression, but it is not yet clearly understood how it works.
There is a growing amount of research into low moods and vitamin D. Research does seem to show a link between low levels of vitamin D in the blood and symptoms of depression. However, research hasn’t yet shown clearly whether low vitamin D levels cause depression, or whether low vitamin D levels develop because someone is depressed. Lack of vitamin D may also be one of many factors that contribute to a depressed mood. There may be many other things that cause depression, which means it’s difficult to say for certain that when depression improves it is vitamin D that is causing the improvement.
However, since vitamin D can greatly benefit your immune system, there is no reason why you should not supplement your diet with it, especially during winter months.