It's hard to be properly nourished when depressed. Sunlight, moderate exercise, some social interaction with positive people and basic nourishment can clear many cases of depression.

The B vitamins (b12 in particular) give energy and have improved some seriously depressed people. Most people are deficient in one or more vitamins unless paying careful attention to diet or supplementing. People overdue it, too, but certain vitamins can be argued to need more than is commonly recommended, like vitamin c.

The hardest part for a depressed person is attending to themselves and that hardest step can break the circle.