Dietary shortages of crucial minerals like zinc may be keeping almost a third of the world's people from optimizing their immune system. Research shows that adequate zinc intake reduces the severity and duration of illness caused by the common cold.
Experts say as many as two billion people around the world have diets deficient in zinc - and studies at Oregon State University and elsewhere are raising concerns about the health implications this holds for infectious disease, immune function, DNA damage and cancer.
The common cold places a heavy burden on society, accounting for approximately 40% of time taken off work and days of school missed by children each year. The idea that zinc might be effective against the common cold first came from a study carried out in 1984, which showed that zinc lozenges could reduce how long symptoms lasted.
The Cochrane Library with data from 15 trials, involving 1,360 people, were included. According to the results, zinc syrup, lozenges or tablets taken within a day of the onset of cold symptoms reduce the severity and length of illness. At seven days, more of the patients who took zinc had cleared their symptoms compared to those who took placebos. Children who took zinc syrup or lozenges for five months or longer caught fewer colds and took less time off school. Zinc also reduced antibiotic use in children, which is important because overuse has implications for antibiotic resistance.
It is recommended that people use simple zinc lozenges without added ingredients or flavorings. Even though such lozenges have a poor taste and can cause nausea on an empty stomach, they work much better.
Since too much zinc can reduce the copper level in the body, hurting immune response, people shouldn't take high doses of the element for longer than four days.
Zinc is naturally found associated with proteins in such meats as beef and poultry, and in even higher levels in shellfish such as oysters. It's available in plants but poorly absorbed from them, raising additional concerns for vegetarians. And inadequate intake is so prevalent in the elderly, Ho said, that they should usually consider taking a multivitamin to ensure adequate levels.
Zinc Deficiency Common
Although researchers have identified zinc deficiency as a primary cause of ailments as we age, it is quite common in the developing world. Even in the United States, about 12 percent of the population is probably at risk for zinc deficiency, and perhaps as many as 40 percent of the elderly, due to inadequate dietary intake and less absorption of this essential nutrient, experts say. Many or most people have never been tested for zinc status, but existing tests are so poor it might not make much difference if they had been.
"Zinc deficiencies have been somewhat under the radar because we just don't know that much about mechanisms that control its absorption, role, or even how to test for it in people with any accuracy," said Emily Ho, an associate professor with the Linus Pauling Institute at OSU, and international expert on the role of dietary zinc.
However, studies have shown that zinc is essential to protecting against oxidative stress and helping DNA repair - meaning that in the face of zinc deficiency, the body's ability to repair genetic damage may be decreasing even as the amount of damage is going up.
Two studies recently published, in the Journal of Nutrition and the American Journal of Clinical Nutrition, found significant levels of DNA damage both with laboratory animals and in apparently healthy men who have low zinc intake. Zinc depletion caused strands of their DNA to break, and increasing the intake of zinc reversed the damage back to normal levels.
The recommended daily allowance is eight milligrams a day for women, 11 for men, and anything over 50 milligrams a day could be considered excessive.
"The consequences of zinc deficiency in adults have been understudied despite the recognition of symptoms of zinc deficiency for decades," researchers wrote in one recent report. "A considerable body of evidence suggests that zinc deficiency may increase the risk of some chronic diseases, including cancer. This link may be attributed to the role of zinc in antioxidant defense and DNA damage repair."