Fruit, Image Courtesy of Grant Cochrane, FreeDigitalPhotos.net
Various vitamin and mineral deficiencies may cause or contribute to anxiety and/or depression. For example, some anxiety sufferers benefit from taking vitamin B supplements and magnesium and calcium supplements. For more information on these benefits, see Vitamin B for Anxiety and Panic Disorder and Magnesium and Calcium for Anxiety.
Vitamin C supplementation may also help those who are under physical or psychological stress, and there is some evidence that vitamin D may benefit those who suffer from depression (major sources of vitamin D are fish and sunshine, and most people get fewer of both these days, making deficiency more common).
Our modern diet, with its emphasis on refined and processed foods, has become heavily weighted toward omega-6 fatty acids and deficient in omega-3s, creating an imbalance. Increasing omega-3 fatty acids either through consuming omega-3 rich foods (fish, walnuts, olive oil, eggs, etc.) or taking fish oil supplements also shows some promise for treating depression and possibly anxiety as well.
There are also some general dietary changes that can be made to treat anxiety. See Food Choices That Reduce Anxiety for more information.
See Anxiety Supplements and Anxiety and Panic Disorder for more information on treating anxiety with natural therapies.