Vitamin D: Egg yolks, fatty fish; fortified milks

Research has revealed a connection between vitamin D and mental health. In one recent meta-analysis involving over 30,000 people, those with low vitamin D levels were more likely to be depressed.

Vitamin D deficiency has also been associated with low moods and poor cognitive performance in older adults.

Our bodies synthesize vitamin D from the sun's ultraviolet light, so most of us can meet at least some of our D needs during sunnier months. Certain factors including darker skin and air pollution, however, can reduce the ability of the sun to produce vitamin D in human skin.

So in the wintertime, it's especially important to seek out vitamin D-rich foods, like fatty fish, eggs and fortified foods and beverages, or vitamin D supplements.