Two nutrients long associated with eye health, lutein and zeaxanthin, are also good for the brain, say researchers at the University of Georgia. Known as the macular carotenoids, they have been proven to enhance vision and to reduce the risk of vision loss in people with age-related macular degeneration (AMD).

Researchers found that lutein and zeaxanthin improved psychological stress levels and reduced levels of cortisol — the stress-related hormone — in the blood.

Fifty-nine healthy, young adults aged 18 to 25 participated in the randomized, double-blind, placebo-controlled study. At the beginning, all had blood cortisol levels measured as well as psychological stress ratings, behavioral measures of mood, and symptoms of sub-optimal health.

Volunteers were then given a daily supplement of 10/2 or 20/4 milligrams of lutein/zeaxanthin, or a placebo. They were tested again at 6 and 12 months.

The results show that supplementation of both doses for 6 months significantly improved psychological stress, serum cortisol, and measures of emotional and physical health compared to placebo.

"This compelling research demonstrates the expanded benefits of supplementing with lutein and zeaxanthin isomers to help address the huge public health concern surrounding elevated stress and cortisol levels," said Abhijit Bhattacharya, President of OmniActive Health Technologies Ltd., producers of Lutemax 2020, the supplement used in the study.

Both lutein and zeaxanthin are carotenoids, which are the pigments that give some foods such as carrots their bright color. They function as antioxidants and numerous studies have found they may lower the risk of many diseases, including heart disease and cancer.

Lutein and zeaxanthin are found in dark green, leafy vegetables and yellow and orange produce. One of the best food sources of both lutein and zeaxanthin is cooked spinach.