Research & Education

Functional roles of Zinc

When you think of zinc, the immune system probably comes to mind first. Supporting immune function is certainly something zinc is needed for, but this unsung mineral has numerous other functional and structural roles throughout the body. (See here for part 1 and part 2 of a primer on zinc.) Zinc may also be beneficial for supporting a healthier body weight in individuals with eating disorders. Let’s take a closer look at this research.

A study by French researchers published earlier this year found that among a cohort of over three hundred patients hospitalized for anorexia nervosa (AN), there were numerous nutrient deficiencies, and zinc deficiency had the highest prevalence: over 64 percent of subjects were found to be zinc deficient. (Other deficiencies identified included copper, selenium, thiamin, and vitamin B12, with a prevalence of 37.1%, 20.5%, 15%, and 4.7, respectively.) These patients were severely malnourished, with a mean weight of 33.7 ± 5.9 kg and a mean body mass index of 12.5 ± 1.7 kg/m2, so it’s not surprising that they had multiple nutrient shortfalls. Out of 374 subjects, only 7 percent had no identified deficiencies. Over 28 percent had one deficiency, 33 percent had two deficiencies, nearly 19 percent had three, and more than 12 percent had deficiencies in four or more nutrients. Regarding zinc, no significant difference was noted between subjects with restrictive-type AN and those with bingeing-purging type.

Worth a closer look is whether zinc deficiency is not just a result of severe food restriction in AN and other eating disorders, but that it may actually be a contributing factor, and whether supplementation may have a role in improving health status in affected patients. The relationship between low zinc status and eating disorders is a complicated one to tease out, and it’s possible it goes both ways: it could be effect and contributing cause. According to one paper, which identified zinc deficiency in 40 percent of subjects with bulimia and 54 percent of those with AN:

“…for a variety of reasons, such as lower dietary intake of zinc, impaired zinc absorption, vomiting, diarrhea, and binging on low-zinc foods, patients with eating disorders may develop zinc deficiency. This acquired zinc deficiency could then add to the chronicity of altered eating behavior in those patients.”

This complexity was acknowledged in a study assessing zinc supplementation versus placebo in healthy controls and subjects with AN or bulimia. The researchers noted that reduced food intake is a major manifestation of zinc deficiency and that some of the results of zinc deficiency overlap with complications of AN and bulimia. Recognizing the potential vicious circle of zinc deficiency as cause or effect in eating disorders, they wrote that zinc deficiency could be a “sustaining factor for abnormal eating behavior in certain eating disorder patients.” Zinc deficiency contributes to alterations in the senses of taste and smell, which could result in decreased appetite and food avoidance, which in turn could exacerbate the deficiency. Writing in the Journal of Orthomolecular Medicine, researchers stated, “The contribution of zinc deficiency to the origin, course, and outcome of Anorexia Nervosa cannot be overestimated.”

Low zinc intake contributes to altered neurotransmitter levels, especially GABA, which may be a contributing factor to the development of AN. Research suggests that zinc supplementation in AN patients may help improve anxiety and depression. (This was seen in a study of adolescents with AN supplemented with 50 mg of elemental zinc.) Zinc has been shown to help increase weight gain in AN patients. In a randomized, double-blind, placebo-controlled trial, compared to placebo, supplementation with 100 mg of zinc gluconate led to double the rate of increase in BMI in female inpatients with AN. A small study of female patients with AN showed that zinc supplementation (45-90 mg/day of zinc sulfate) supported weight gain in 17 of 20 patients. Thirteen subjects who had been amenorrheic had restoration of menstruation within 1-17 months of beginning zinc supplementation. Worth noting, none of the subjects lost further weight after initiating zinc therapy. Further research in this area is still needed.

Individuals with identified zinc deficiency may benefit from supplementation, as may those who are vegetarians, habitually consume alcohol, or who have a low intake of zinc-rich foods. Foods high in zinc include red meat and other dark meats, shellfish, and certain beans, legumes, and nuts. The zinc in animal-sourced foods is more bioavailable than that in plant-sourced foods, because the presence of dietary fiber and phytic acid may impair zinc absorption from the latter.