Walnuts contain melatonin, research shows


The next time you reach for salad greens and dressing, you might consider adding some walnuts. New research out of the Health Science Center shows that walnuts contain a fair amount of melatonin, a hormone that protects our cells against oxidative damage.

“Relatively few foods have been examined for their melatonin content,” said Russel Reiter, Ph.D., professor of cellular and structural biology at the Health Science Center. “Our studies demonstrate that walnuts contain melatonin, that it is absorbed when it is eaten, and that it improves our ability to resist oxidative stress caused by toxic molecules called free radicals.”

The research is reported in the September issue of the journal Nutrition.

Many diseases of aging, including cataracts, Alzheimer’s disease and Parkinson’s disease, have a free-radical component, Dr. Reiter said. A primary theory of aging states that aging and its associated degenerative changes are consequences of free-radical damage. Melatonin acts like a cellular “Pac-Man” gobbling up free radicals before they can cause harm.

“Melatonin is found in all vertebrates and invertebrates, even in algae, slime molds and bacteria,” Dr. Reiter said. “In 1995, a couple of publications appeared showing that it also is present in plants. So, we not only produce it in our bodies, but we eat it in our diets.”

Walnuts also contain large amounts of omega-3 fatty acids, which have been shown to inhibit certain types of cancer and to be heart healthy. Melatonin also has been shown to inhibit certain types of cancer. “Maybe these two ingredients complement each other,” Dr. Reiter said. He plans an upcoming study to explore this synergistic effect.

Melatonin was first described in corn, tomatoes and potatoes, which have very little of it. Walnuts are a different story. “How many walnuts would you have to eat a day to benefit in terms of their melatonin content? We really don’t know,” Dr. Reiter said. “The bottom line is, now we know that walnuts have another ingredient that is healthy, namely, melatonin.”

Eating a good, nutritious diet containing a variety of nutrient-rich foods is undoubtedly better than trying to get those beneficial ingredients from supplements. “It’s the package deal,” Dr. Reiter said. “In walnuts it’s not only the melatonin that is healthy, but the other ingredients. It’s really the composite of the nut that makes it healthy, not one ingredient.”

Melatonin is perhaps more famous as a sleep aid. The pineal gland in the brain secretes a little of it during the day and more at night. The nighttime rise is most important. As we get older, our nighttime melatonin levels wane, often wreaking havoc on regular sleep patterns.

Free-radical damage increases as we age, while melatonin decreases. “I’m not going to suggest that if we boost our melatonin level we can defer age-related conditions,” Dr. Reiter said. “But it is worth asking this question: Is the loss of melatonin, an important anti-oxidant, of any consequence in terms of us developing free-radical-related diseases? In the lab, we can use pure melatonin to forestall a lot of free-radical damage.”

For example, adding melatonin to the diet of newborn rats that are susceptible to cataracts prevents cataracts from forming, he observed.

The finding that walnuts contain melatonin is important. “We don’t know the half of it yet,” Dr. Reiter said.

The California Walnut Industry provided a grant to support Dr. Reiter’s research.

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