Zinc

Does zinc help when intake is low?

This is where the evidence is most consistent. In low-income countries where zinc deficiency is common, a 2016 Cochrane review of six trials in 5,193 children aged 2 to 59 months found that 10 to 20 mg zinc for up to 20 months lowered the incidence and prevalence of pneumonia compared with placebo. 1

The World Health Organization and UNICEF recommend 10 or 20 mg zinc per day, depending on age, for 10 to 14 days to treat acute diarrhea in children. Because most of these trials ran in low-income countries, the effect may be marginal in well-nourished children. 1

An umbrella review of 43 published reviews reached the same picture: in children, zinc supplements reduced diarrhea and pneumonia, improved zinc deficiency and supported growth. 2

Does zinc shorten a cold?

A 2024 Cochrane review pooled 34 trials with 8,526 participants. In people who already had a cold, zinc may shorten it by about 2.4 days on average (8 trials, 972 people), but the certainty was low and results varied widely between trials. Whether zinc makes symptoms milder is uncertain. 3

Taken to prevent colds, zinc made little or no difference to the risk of catching one (9 trials, 1,449 people, low certainty). 3

Most treatment trials used lozenges, mainly zinc gluconate or acetate. Gluconate lozenges were given at 45 to 276 mg zinc per day for 4.5 to 21 days, far above the daily upper limits for long-term intake. An earlier review found that lozenges providing more than 75 mg per day shortened colds while lower doses did not. 1 3

People treated with zinc reported more non-serious side effects than people given placebo. 3

Does zinc lower inflammation and oxidative stress?

Several meta-analyses report that zinc changes blood markers. One pooled 35 randomized trials with 1,995 adults and found lower C-reactive protein (CRP) and neutrophil counts and higher CD4 cell counts, with no effect on total white cells or lymphocytes. 4

Another analysis of 25 trials with 1,428 adults found small reductions in CRP (0.03 mg/L) and interleukin-6 and in malondialdehyde, a marker of oxidative damage, plus a rise in total antioxidant capacity. The trials differed a lot from each other. 5

A third review of 23 trials lasting 4 to 24 weeks found higher glutathione and total antioxidant capacity with zinc, an effect on superoxide dismutase only after correcting for publication bias, and no effect on glutathione peroxidase. 6

Two small trials illustrate the type of evidence. In 40 healthy adults aged 56 to 83, 45 mg zinc gluconate daily for 6 months lowered CRP, interleukin-6 and oxidative-stress markers compared with placebo. In 40 young women with obesity, 30 mg zinc gluconate for 8 weeks lowered CRP and interleukin-6 but did not change leptin or adiponectin. 7 8

These are laboratory markers, not illnesses. None of these studies shows that the changes translate into fewer heart attacks, infections or other health events. 4 5 6

Does zinc help acne?

A 2020 meta-analysis found that people with acne had lower serum zinc than people without it. Treatment with oral or topical zinc reduced the number of inflammatory papules compared with no zinc, alone or added to other treatment, without a significant difference in side effects. 9

A systematic review of 22 trials across inflammatory skin conditions found a benefit in 10 of 14 acne studies and in all 3 studies of hidradenitis suppurativa. Single studies in psoriasis and rosacea showed no benefit. The authors called the acne evidence preliminary and asked for larger studies with comparable methods. 10

Does zinc improve sperm quality?

Infertile men tend to have less zinc in seminal fluid than fertile men. A 2016 meta-analysis of 20 studies confirmed this and reported that zinc supplements increased semen volume, sperm motility and the share of normally shaped sperm in infertile men. Smaller observational studies link seminal zinc with sperm count and shape, which shows an association, not cause and effect. 11 12

The largest trial points the other way. In the US FAZST trial, 2,370 men from couples planning infertility treatment took 30 mg zinc plus 5 mg folic acid or placebo daily for 6 months. Sperm concentration, motility, morphology and live birth rates did not differ, DNA fragmentation was slightly higher with the supplement, and digestive complaints were more common. 13

Does zinc raise testosterone or libido?

A 2023 systematic review on zinc and testosterone included 38 papers, but only 8 were clinical studies and 30 were animal studies. It concluded that zinc deficiency lowers testosterone and that the effect of supplements depends on baseline zinc and testosterone levels, dose, form and duration. 14

The review did not assess libido or sexual performance. Claims about these outcomes therefore rest on the testosterone link rather than on trials that measured them. 14

Does zinc lower cholesterol?

A 2015 meta-analysis of 24 studies (14,515 participants, 15 to 240 mg zinc per day for 1 month to 7.5 years) found lower total cholesterol, LDL cholesterol and triglycerides with zinc, and no significant change in HDL cholesterol. Some included studies combined zinc with other micronutrients, and results varied considerably between studies. 15

In people with type 2 diabetes, a meta-analysis of nine trials found lower triglycerides and total cholesterol but no change in LDL or HDL cholesterol. Doses of 50 mg or more taken for weeks can lower HDL cholesterol. 1

Does zinc help with blood sugar and metabolism?

Observational studies link higher zinc intake with a 13% lower risk of type 2 diabetes. A 2015 Cochrane review found only three small prevention trials (128 participants) and could not draw conclusions. 1

Later meta-analyses in people with type 2 diabetes reported lower fasting glucose, insulin resistance and HbA1c with zinc. NIH ODS still judges the evidence insufficient to support zinc for preventing or managing type 2 diabetes. 1

Does zinc protect eyesight in macular degeneration?

In the AREDS trial, 4,757 people aged 50 to 80 at high risk of advanced age-related macular degeneration took a daily supplement with 80 mg zinc (as zinc oxide), 2 mg copper, vitamin C, vitamin E and beta-carotene, or placebo, for 5 years. The supplement lowered the risk of advanced disease by 25%. 1

AREDS2 suggested that a formula with 25 mg zinc worked as well, but the researchers considered this preliminary. The US National Eye Institute recommends the 80 mg formulation. The trials enrolled people who already had intermediate disease or advanced disease in one eye, and NIH ODS advises people with the condition to discuss zinc intake and these formulations with their doctor. 1

Does zinc affect thyroid function?

A meta-analysis of 32 observational studies found lower zinc levels in people with hypothyroidism than in healthy controls. This does not show that low zinc causes thyroid disease or that supplements correct it. 16

In an open-label trial in 40 children with autoimmune thyroiditis, 25 mg zinc daily for 12 weeks did not change thyroid function tests or thyroid antibodies, although the zinc group needed fewer levothyroxine dose increases. 17

What the evidence does not show

The research does not show that extra zinc prevents colds, that it lowers overall mortality in adults, or that large doses protect against prostate cancer: in the umbrella review, 100 mg per day showed no benefit for prostate cancer risk. 2 3

Benefits seen in children with poor zinc status or in people with a diagnosed condition do not automatically carry over to healthy, well-fed adults. 1

Who was studied, and what are the limits?

Cold trials were mostly in adults in the United States, and most were at unclear or high risk of bias in at least one area. Zinc forms, doses, routes and outcomes varied widely, and several trials reported incompletely. 3

The strongest child-health findings come from low-income countries where deficiency is common. Much of the marker research consists of trials with a few dozen participants lasting weeks to months. 1 7 8