Food is medicine: The science behind zinc and other supplements for immune health
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Key takeaways:
- Research indicates that zinc may offer benefits for immune health, but the evidence is not conclusive.
- Other ingredients popular in immune supplements, like vitamin D, seem to be ineffective in healthy adults.
The evidence on popular supplements claiming to boost the immune system is shaky, but zinc may offer benefits for some, according to experts.
Research has indicated that immune health products represent an estimated 10% of all dietary supplement sales in the United States.
“Many people take dietary supplements during the cold and flu season, hoping these products will support or protect their immune system and reduce the risk for illness,” LaVerne L. Brown, PhD, director of the resilience and health studies program at the NIH’s office of dietary supplements, told Healio. “Zinc, vitamin C, vitamin D, probiotics, echinacea and elderberry are some of the more common ingredients in these types of supplements.”
Zinc — a nutrient that can be found in various foods, such as poultry, beef, pork, lobster, crab, oysters, nuts, whole grains, dairy products and beans — “is required for proper growth and development during pregnancy, infancy and childhood,” Brown said.
Zinc is also important for helping wounds heal, making proteins and DNA, and plays a role in the functioning of taste buds, she said. In addition, “zinc plays a role in immune system health, and a deficiency can adversely affect immune function."
“Zinc and other vitamins and minerals all have essential roles in human health,” Brown said.
Carol J. Haggans, MS, RD, a scientific and health communications consultant at the NIH’s office of dietary supplements, said that supplements “can increase nutrient intakes if someone consumes insufficient amounts from their diet.”
“Research suggests that supplementation with some nutrients might modestly benefit immune health,” she said.
Summary of evidence on zinc
Brown and another scientist with the NIH’s office of dietary supplements recently co-authored a systematic review evaluating 39 randomized controlled trials that assessed the current research on certain ingredients that were popular in supplements claiming to promote immune health (echinacea, elderberry, garlic, zinc and vitamins A, C, D and E). Focusing on outcomes related to resilience rather than disease endpoints, Brown and colleagues did not find much evidence to indicate that taking the ingredients before getting sick would diminish the duration or severity of any acute respiratory infection.
“Claims made for boosting the immune system on dietary supplement products and the ingredients contained in those products do not appear to have overall strong scientific evidence as of yet for the otherwise healthy consumer looking to maintain health, resist getting sick, or recover quickly,” they wrote. “As we move toward a vision of health promotion and resilience rather than a sole focus on disease prevention and treatment, further work in this area of dietary supplements is of utmost importance.”
However, other research has indicated that zinc levels specifically may be important for immune health. For example, a 2018 systematic review and meta-analysis found that patients with autoimmune diseases had significantly lower levels of zinc concentrations in both serum and plasma compared with the control group.
Additional research has examined whether zinc supplementation affects mortality in patients with COVID-19. A 2022 meta-analysis revealed that in-hospital mortality among patients treated with zinc supplementation and those treated without, “varied and amounted to 21.6% vs. 23.04% difference (OR = 0.71; 95% CI, 0.62–0.8).” Also, 28-day to 30-day COVID-19-related mortality was 7.7% among patients treated with the supplement (OR = 0.61; 95% CI, 0.35-1.06) compared with 11.9% in patients who were not. Another 2022 systematic review and meta-analysis also found that zinc supplementation resulted in a significantly lower risk for COVID-19 mortality compared with the control group (pooled OR = 0.57; 95% CI, 0.43-0.77).
Based on these findings, some researchers recommend considering zinc as an adjunct therapy for patients with COVID-19. However, the NIH COVID-19 treatment guidelines stated that there was insufficient evidence for the COVID-19 Treatment Guidelines Panel “to recommend either for or against the use of zinc for the treatment of COVID-19.”
Other supplements for immune function
Brown said that vitamin D “was one of the top ingredients found in dietary supplements with immune health claims.” Although it is well-known for its benefits on bone health and calcium absorption, “scientific studies do not show strong evidence of benefit of vitamin D supplementation in healthy adults with adequate vitamin D levels.”
Brown also noted that some nonessential ingredients, including garlic, echinacea, probiotics and other herbs, “are being investigated for their effects on the immune system” but added that “the nutritional value/role of these ingredients have not been established.”
Ultimately, primary care physicians should evaluate a patient’s nutritional status to decide if a supplement might benefit their health, Haggans said.
“Asking patients about their typical daily diet and whether they exclude any food groups (dairy, animal products, gluten, etc.) can help determine if they might obtain insufficient amounts of some nutrients,” Haggans said. “For example, people who follow a vegan diet might have trouble getting enough vitamin D and zinc.”
Those who have alcohol use disorder or gastrointestinal disorders may also be deficient in zinc, and those who smoke may have lower vitamin C levels, she said.
However, PCPs should also consider some of the potential downsides with immune-boosting supplements, Haggans said.
“Most, but not all, nutrients have tolerable upper intake levels (ULs) and can cause health problems if consumed in excess,” Haggans said. “For example, excessive amounts of zinc can cause dizziness, headaches and an upset stomach. It can also decrease the body’s ability to absorb copper. Patients should strive to consume recommended amounts of nutrients without exceeding ULs, unless specifically warranted for medical treatment.”
It is also important to consider potential medication interactions, Haggans said.
“For example, vitamin D and calcium in combination with thiazide diuretics could lead to hypercalcemia due to decreased urinary calcium excretion and increased intestinal calcium absorption,” she said. “And echinacea might induce cytochrome P450 activity, which could reduce levels of some drugs metabolized by these enzymes.”
The NIH’s Dietary Supplement Label Database contains information from the labels of over 183,000 dietary supplements on the market in the U.S., and it can help primary care providers and consumers find and compare products.
The NIH’s Office of Dietary Supplements also offers other resources for health care providers and consumers. To learn more about immune-boosting supplements and other products, check out the NIH’s Office of Dietary Supplements Fact Sheets.
Editor’s Note: Healio is highlighting the clinical value of various supplements. See other installments of the series here:
References:
- Abioye AI, et al. BMJ Glob Health. 2021;doi:10.1136/bmjgh-2020-003176.
- COVID-19 treatment guidelines. https://www.covid19treatmentguidelines.nih.gov/therapies/supplements/zinc/. Accessed Feb. 23, 2024.
- Crawford C, et al. Nutrients. 2022;doi:10.3390/nu14214604.
- Olczac-Pruc M, et al. Ann Agric Environ Med. 2022;doi: 10.26444/aaem/155846.
- Penzak SR, et al. Pharmacotherapy. 2010;doi:10.1592/phco.30.8.797.
- Robien K, et al. Nutr Clin Pract. 2013;doi: 10.1177/0884533612467824.
- Sanna A, et al. Nutrients. 2018;doi:10.3390/nu10010068.
- Tabatabaeizadeh SA. Eur J Med Res. 2022;doi:10.1186/s40001-022-00694-z.