The growth factors that are essential for building the brain's nerve cell connections need nutrients to function. Numerous studies have shown that a lack of nutrients and, as a result, a lack of nerve growth factors, leads to nerve cell shrinkage and death. These effects may interfere with proper signaling between nerve cells, leading to symptoms of mood disorders.
Antidepressants have been shown to increase the brain growth factor levels somewhat, but several studies have shown that nutrients such as calcium and zinc appear to do a better job.