The Latest Research on Zinc

Photo: Olga Chernyak/Shutterstock.com

Although its importance for humans was not determined until the early 1960s, zinc has quickly become a well-known essential mineral. While researchers continue to investigate that association and many other potential areas in which zinc may play a role, let us explore some of the other recent findings of the relationship between zinc and human health. This is by no means comprehensive, but I hope it provides insight into some of the interesting links between zinc and health that researchers are exploring.

Zinc 101

First, let us take a quick look at the basics. Zinc binds to more than 300 enzymes and 2000 transcriptional factors, meaning it is involved in a lot of different body processes, biochemical pathways, and cellular functions including:

Most zinc is found in skeletal muscle (approximately 60 percent), while the second most abundant location is bone (30 percent). The liver and skin have around 5 percent each.

The current US daily RDA for zinc for adults is 8 mg for women and 11 mg for men. About 15 percent of the US population has an inadequate dietary intake for zinc; including supplementation dropped that to 11 percent, based on data from the NHANES 2005-2016 studies.

For the elderly population, that number is higher. Based on a systematic review of studies in Western countries, for the elderly population still living in the community, 31 percent of women and 49 percent of men were deficient for zinc, while 50 percent of women and 66 percent of men living in some type of institutional care had zinc deficiencies.

The classic symptoms of zinc deficiency include loss of taste and smell, memory problems, immune dysfunction and increased susceptibility to infectious disease, dermatitis, diarrhea, alopecia, and decreased spermatogenesis. Zinc deficiency is associated with many conditions, including:

Additionally, it’s considered as one treatment for childhood diarrhea in the WHO guidelines. A Cochrane review concluded that zinc supplementation may shorten the duration of diarrhea in children, benefitting children older than 6 months of age in areas where malnutrition and/or zinc deficiency is common but not necessarily for children at low risk of zinc deficiency.

Due to its wide-ranging influence in the body based on its role in enzymes and transcriptional factors, there are many different areas in which researchers are looking to further identify zinc and zinc deficiency’s role in health and disease. Let us check out some of the latest research in a few of these areas.

Immunity and Zinc

One reason for zinc’s popularity is its association with immunity. Long before COVID-19, it has been included in immune-supporting supplements, and researchers have studied it for its use for childhood infectious diseases and the common cold.

One study on elderly patients found that supplementing with a multi-vitamin/multi-mineral (1 gram per day of vitamin C and 10 mg per day of zinc along with additional vitamins and minerals) led to an increased level of vitamin C and zinc in the blood. While there were no changes to the functional outcomes of neutrophils nor in killing of the pathogen X. aureus, there was a statistically significant decrease in the severity and length of the reported illnesses by the participants taking the supplement compared to the controls.

A recent cell study found that the ratio of interferon-gamma, a key component of the immune system’s defense toward intracellular pathogens, to secreted protein is dependent on zinc, meaning it regulates post-transcriptional interferon production. A reduction in interferon-gamma could lead to an impaired immune system, and excess could contribute to the development of autoimmune disorders. Zinc may also modulate Nrf2, which regulates antioxidant proteins in the body.

Zinc and the Brain

As one of the most abundant minerals found in the brain, it should come as no surprise that zinc status impacts brain health and cognitive function. Among its roles in the brain, it maintains oxidative balance and modulates neuronal survival. Ionic zinc exists within synaptic vesicles, releasing during neuronal activity.

A recent study looked at the link between zinc deficiency and neuronal death. There was an increase in apoptosis rate in cells with zinc deficiency, which led to alterations in neurotransmitters, specifically an increase in aspartic acid and a decrease in glutamate, glycine, and GABA. Zinc supplementation reversed these changes. While this is a mechanistic study and as such may not adequately reflect real-world scenarios, it does point to one possible reason for the impact of zinc deficiency on alterations to mood.

Another study found a correlation between zinc deficiency and depression in an elderly population, with 72.4 percent of the participants having an inadequate dietary intake of zinc. Those in the third tertial of serum zinc levels had a 51 percent reduced risk of depression compared to those in the first tertial.

One replication and meta-analysis study found serum zinc was significantly lower in patients with Alzheimer’s disease, and copper levels were significantly higher, thus correlating to higher copper/zinc ratios. The researchers postulated a possible causal connection between changes in zinc and copper levels and the pathogenesis of AD.

Copper/Zinc Ratio

When talking about zinc, we cannot overlook its very important relationship with copper. I previously wrote a blog about the importance of having the right balance of copper and zinc and its role in oxidative stress, inflammation, immune health, brain health, and more. In fact, one study found that higher plasma copper/zinc ratios were a predictor for all-cause mortality as well as an indicator of increased inflammation. I found some additional research that caught my attention, which is highlighted below.

In one study, having higher copper levels and lower zinc levels correlated with a higher risk of ectopic pregnancy, likely due to oxidative stress, with the copper/zinc ratio having a stronger association than either mineral alone.

Additionally, a meta-analysis found that increased serum levels of copper, decreased levels of zinc, and a higher copper/zinc ratio correlated with a higher risk of breast cancer. There’s also an association between higher copper/zinc ratios and Hodgkin’s disease prognosis and clinical stage.

A recent study based on NHANES data (from 1976-1980, which is a limitation to the study) found that individuals with IBS had higher copper to zinc ratios (average of 1.7 compared to 1.55) and had a higher risk of having levels above 1.8.

Another study found that sickle-cell disease patients had significantly higher copper to zinc ratios compared to healthy controls. They also had higher iron and copper levels, and the researchers felt that the copper to zinc ratio may also be used as a marker for oxidative stress in this population.

The copper/zinc ratio in childhood is negatively associated with educational attainment in adulthood, with higher ratios associated with lower GPAs, less schooling, and a reduced likelihood of going to university.

In my previous post, I wrote about an article discussing the connection between the copper/zinc ratio and sleep duration in men. There is also an inverse association between optimal sleep duration and copper/zinc ratios in adult women. This effect may have to do with a relationship between zinc and melatonin, as one animal study found a correlation between zinc levels and melatonin levels, with supplementation raising melatonin levels.

Diabetes and Heart Disease

Zinc status also plays a role in blood sugar regulation and heart health. One study found an association between reduced dietary intake of zinc and metabolic syndrome. Those with metabolic syndrome also have alterations in zinc metabolism including higher urinary zinc excretion and higher erythrocyte zinc regardless of intake, likely due to increased oxidative stress and inflammation. There is also an association between reduced zinc levels and poor glycemic control in those with type 2 diabetes, as well as increased risk of DNA damage due to oxidative stress.

A randomized, double-blind, placebo-controlled trial found that supplementing with 50 mg of zinc gluconate for 8 weeks increased the insulin levels and superoxide dismutase (SOD) gene expression and enzyme activity. Additionally, those taking zinc had a meaningful reduction in other markers of diabetes, including HbA1c, HOMA-IR, fasting blood glucose, triglycerides, and total cholesterol.

In terms of heart health, a recent meta-analysis found a significant association between heart failure and low levels of serum zinc. Another study found that decreased serum zinc levels in patients with heart failure correlated with a higher mortality risk as well as reduced exercise capacity. It may even be a reversible cause of heart failure based on a case study, although more research is needed.

Zinc may be protective against atherosclerosis through reducing inflammation and oxidative stress. One study found that six months of supplementation led to a decrease in many inflammatory and oxidative stress markers associated with atherosclerosis.

Additional Zinc Findings

Some other studies focusing on a range of areas of health caught my attention that I wanted to share.

Zinc deficiency in infants and young children is correlated with growth and development issues. Studies have found some benefit of zinc supplementation in this population, including to head growth in infants between 23 and 28 weeks. Furthermore, in children, zinc deficiency along with iron deficiency is related to memory deficits.

Low levels of magnesium and zinc have also been shown to correlate with an increased risk of restless leg syndrome in pregnancy.

There’s also an association with low dietary intakes of zinc and an increased risk of chronic kidney disease development in those with normal renal function.

One study found a correlation between zinc deficiency and time between flare-ups in inflammatory bowel disease, especially Crohn’s disease.

There is a connection between low levels of zinc and other minerals with hemophilia, which were then associated with worse symptoms and a poorer quality of life.

A recent Cochrane review on multivitamin antioxidant vitamin and mineral supplementation found some benefit in delaying age-related macular degeneration progression, with zinc specifically showing a slow-down of progression.

Food Sources of Zinc

This exciting and interesting research reinforces the importance of getting sufficient zinc, preferably through food. Luckily, there are many options for finding dietary sources of this essential mineral. In general terms, seafood, meat, nuts and seeds, whole grains, and legumes are some of the best sources of dietary zinc. Some of the richest sources of zinc in order from greatest to least include:

  • Oysters
  • Crab
  • Beef
  • Lobster
  • Porkchop
  • Baked beans
  • Chicken
  • Pumpkin seeds
  • Cashews
  • Chickpeas
  • Milk
  • Almonds
  • Kidney beans

More recently, it was published that rooibos tea also provides a source of zinc. Humans only absorb about 33 percent of the zinc consumed, although there are key factors that impact absorption:

While there are many options for dietary intake of zinc and it is possible to achieve sufficient levels through food alone, for some people, supplementation may be necessary. In my previous post on zinc and copper, I discussed in detail what you need to know about supplementing. In general, you want to be careful to avoid with excessive levels of zinc and/or an imbalance of the copper/zinc ratio. The tolerable upper intake level for zinc is 40 mg for adults, and taking excessive levels of zinc can lead to diarrhea, abdominal cramps, and vomiting.

If you feel that you need to boost your zinc intake to help with one or more of the health conditions discussed in this post, then talk with your doctor, dietician, nutritionist, or another member of your healthcare team about whether supplementing is right for your circumstances.

 

Previous

Next

Submit a Comment

Your email address will not be published. Required fields are marked *

X