Zzzz-Zinc

It is a measure of the mystery of sleep that despite extraordinarily sophisticated research tools, scientists are still trying to figure out how this most basic of biological functions comes about. All animals sleep. And they fall apart if they don't. Human beings chronically deprived of sleep are subject to cardiovascular disease, metabolic disruption leading to obesity and diabetes, immune malfunction, and mental disorders from depression to Alzheimer's disease. Sleeping too little (or too much) shortens lifespan.

The body restores and heals itself during sleep. Memory consolidates. But what triggers sleep and what keeps it going? Researchers were recently surprised to discover that the mineral zinc seems to be an essential part of the process.

The second most abundant trace mineral in the human body—after iron—zinc is a cofactor in more than 300 enzymes and 1,000 transcription factors that carry out genetic instructions. Zinc is essential for bone growth, prostate health and male fertility, taste perception, wound healing, and cognitive function.

In the brain, the micronutrient modulates neural transmission and neural plasticity. It is also necessary for neurogenesis, notably in the hippocampus, essential to the acquisition and storage of memory.

And now, researchers find, zinc also regulates sleep. It's not clear how, but it seems to abet slow-wave sleep, the nondreaming, deep sleep of physical restoration and memory consolidation. Zinc doesn't seem to trigger sleep, but adequate levels of zinc in the blood shorten the time it takes to fall asleep (sleep latency), increase the overall amount of sleep, and assure sleep quality and efficiency (time spent asleep when in bed).

In 2009, researchers examining 890 healthy residents of Jinan, China, discovered that serum zinc levels varied with the amount of sleep subjects got, and those with the highest concentrations of zinc were those sleeping a normal 7 to 9 hours a night.

Since then, a number of other studies in different populations have linked optimal sleep time to high levels of zinc. But cross-sectional studies can show only correlation. Longitudinal studies add evidence of causation. In a study of 1,295 young children followed for nine years, other researchers in China found that adolescents with higher blood zinc concentrations were more likely to have normal sleep quality—significant because up to 70 percent of adolescents worldwide report disturbed sleep-wake patterns. As zinc concentrations increased, the likelihood of insufficient sleep and sleep disturbances decreased.

Among preschool-age children, low blood zinc levels predicted an increase in the likelihood of poor sleep quality and poor sleep efficiency in adolescence. Zinc status in early life may have a particularly long-lasting effect on sleep regulation.

Evidence has been accruing from other studies as well. An analysis of nutritional data from 5,000 Americans shows that those who sleep the least consume significantly less zinc than normal or long sleepers. And zinc supplements, typically combined with other nutrients, given to varied groups significantly improved their sleep time and sleep quality.

But so far, the most convincing evidence that zinc, consumed in food or supplement, is a sleep modulator comes from a Japanese study of mice fed a yeast extract fortified with either zinc or other minerals. Only the zinc-fed mice experienced a "drastic reduction" in movement at sleep time, and electrical brain recordings showed an increase in the amount of high-quality slow-wave sleep.

The researchers believe that once a certain blood level of zinc is reached, it crosses into the brain and activates signaling pathways to promote sleep. "Our data," they say, "open the way to new types of food supplements designed to improve sleep."

Where the Zinc Is

• Muscle (harbors more than 50 percent
• of the body’s zinc)
• Bone
• Eye
• Brain, especially the hippocampus
• Prostate
• Liver

The Many Roles of Zinc

• Is a cofactor for more than 300 enzymes, many in the central nervous system.
• Regulates gene expression and stabilizes DNA
• Modulates neurotransmitter activity
• Influences all components of the immune response
• Modulates secretion and utilization of insulin
• Stimulates adult neurogenesis
• Is essential to brain development (mechanism unknown)
• Acts as an antioxidant

Think Zinc

• Zinc is the second most common trace element in the human body, after iron.
• Supplements of zinc, often combined with other nutrients, improve sleep time.
• In depressed patients, low serum zinc levels may be a biomarker for resistance to antidepressant drugs.
• Studies show that zinc is required for the efficacy of antidepressant drugs.
• Zinc deficiency increases the oxidative stress on mitochondria.
• Zinc is essential for prostate function and male fertility.
• Because it is a component of so many enzymes, zinc is found throughout the body, but it is especially concentrated in muscle, bone, and the liver.
• Normal growth during development depends on adequate levels of zinc.
• Appetite regulation requires zinc; deficiency of the mineral leads to decreased appetite.
• The RDA for zinc is 11 mg/day for males over age 14 and 8 mg/day for females 19 and older.
• Foods with high levels of zinc include oysters, red meat, and wheat germ.
• Signs of zinc deficiency include growth retardation, delayed sexual maturation, eye and skin lesions, and appetite loss.