zinc
A Potential New Way to Prevent Noise-Induced Hearing Loss: Trapping Excess Zinc
Posted on by Dr. Monica M. Bertagnolli
Hearing loss is a pervasive problem, affecting one in eight people aged 12 and up in the U.S.1 While hearing loss has multiple causes, an important one for millions of people is exposure to loud noises, which can lead to gradual hearing loss, or people can lose their hearing all at once. The only methods used to prevent noise-induced hearing loss today are avoiding loud noises altogether or wearing earplugs or other protective devices during loud activities. But findings from an intriguing new NIH-supported study exploring the underlying causes of this form of hearing loss suggest it may be possible to protect hearing in a different way: with treatments targeting excess and damaging levels of zinc in the inner ear.
The new findings, reported in the Proceedings of the National Academy of Sciences, come from a team led by Thanos Tzounopoulos, Amantha Thathiah, and Chris Cunningham, at the University of Pittsburgh.2 The research team is focused on understanding how hearing works, as well as developing ways to treat hearing loss and tinnitus (the perception of sound, like ringing or buzzing, that doesn’t have an external source), which both can arise from loud noises.
Previous studies have shown that traumatic noises of varying durations and intensities can lead to different types of damage to cells in the cochlea, the fluid-filled cavity in the inner ear that plays an essential role in hearing. For instance, in mouse studies, noise equivalent to a blasting rock concert caused the loss of tiny sound-detecting hair cells and essential supporting cells in the cochlea, leading to hearing loss. Milder noises comparable to the sound of a hand drill can lead to subtler hearing loss, as essential connections, or synapses, between hair cells and sensory neurons are lost.
To better understand why this happens, the research team wanted to investigate the underlying cellular- and molecular-level events and signals responsible for inner ear damage and irreversible hearing loss caused by loud sounds. They looked to zinc, an essential mineral in our diets that plays many important roles in the body. Interestingly, zinc concentrations in the inner ear are highest of any organ or tissue in the body. But, despite this, the role of zinc in the cochlea and its effects on hearing and hearing loss hadn’t been studied in detail.
Most zinc in the body—about 90%—is bound to proteins. But the researchers were interested in the approximately 10% of zinc that’s free-floating, due to its important role in signaling in the brain and other parts of the nervous system. They wanted to find out what happens to the high concentrations of zinc in the mouse cochlea after traumatic levels of noise, and whether targeting zinc might influence inner ear damage associated with hearing loss.
The researchers found that, hours after mice were exposed to loud noise, zinc levels in the inner ear spiked and were dysregulated in the hair cells and in key parts of the cochlea, with significant changes to their location inside cells. Those changes in zinc were associated with cellular damage and disrupted communication between sensory cells in the inner ear.
The good news is that this discovery suggested a possible solution: inner ear damage and hearing loss might be averted by targeting excess zinc. And their subsequent findings suggest that it works. Studies in mice that were treated with a slow-releasing compound in the inner ear were protected from noise-induced damage and associated hearing loss. The treatment involves a chemical compound known as a zinc chelating agent, which binds and traps excess free zinc, thus limiting cochlear damage and hearing loss.
Will this strategy work in people? We don’t know yet. However, the researchers report that they’re planning to pursue preclinical safety studies of the new treatment approach. Their hope is to one day make a zinc-targeted treatment readily available to protect against noise-induced hearing loss. But, for now, the best way to protect your hearing while working with noisy power tools or attending a rock concert is to remember your ear protection.
References:
[1] Quick Statistics About Hearing. National Institute on Deafness and Other Communication Disorders.
[2] Bizup B, et al. Cochlear zinc signaling dysregulation is associated with noise-induced hearing loss, and zinc chelation enhances cochlear recovery. PNAS. DOI: 10.1073/pnas.2310561121 (2024).
NIH Support: National Institute on Deafness and Other Communication Disorders, National Institute on Aging, National Institute of Biomedical Imaging and Bioengineering
Study Finds No Benefit for Dietary Supplements
Posted on by Dr. Francis Collins
More than half of U.S. adults take dietary supplements [1]. I don’t, but some of my family members do. But does popping all of these vitamins, minerals, and other substances really lead to a longer, healthier life? A new nationwide study suggests it doesn’t.
Based on an analysis of survey data gathered from more than 27,000 people over a six-year period, the NIH-funded study found that individuals who reported taking dietary supplements had about the same risk of dying as those who got their nutrients through food. What’s more, the mortality benefits associated with adequate intake of vitamin A, vitamin K, magnesium, zinc, and copper were limited to food consumption.
The study, published in the Annals of Internal Medicine, also uncovered some evidence suggesting that certain supplements might even be harmful to health when taken in excess [2]. For instance, people who took more than 1,000 milligrams of supplemental calcium per day were more likely to die of cancer than those who didn’t.
The researchers, led by Fang Fang Zhang, Tufts University, Boston, were intrigued that so many people take dietary supplements, despite questions about their health benefits. While the overall evidence had suggested no benefits or harms, results of a limited number of studies had suggested that high doses of certain supplements could be harmful in some cases.
To take a broader look, Zhang’s team took advantage of survey data from tens of thousands of U.S. adults, age 20 or older, who had participated in six annual cycles of the National Health and Nutrition Examination Survey (NHANES) between 1999-2000 and 2009-2010. NHANES participants were asked whether they’d used any dietary supplements in the previous 30 days. Those who answered yes were then asked to provide further details on the specific product(s) and how long and often they’d taken them.
Just over half of participants reported use of dietary supplements in the previous 30 days. Nearly 40 percent reported use of multivitamins containing three or more vitamins.
Nutrient intake from foods was also assessed. Each year, the study’s participants were asked to recall what they’d eaten over the last 24 hours. The researchers then used that information to calculate participants’ nutrient intake from food. Those calculations indicated that more than half of the study’s participants had inadequate intake of vitamins D, E, and K, as well as choline and potassium.
Over the course of the study, more than 3,600 of the study’s participants died. Those deaths included 945 attributed to cardiovascular disease and 805 attributed to cancer. The next step was to look for any association between the nutrient intake and the mortality data.
The researchers found the use of dietary supplements had no influence on mortality. People with adequate intake of vitamin A, vitamin K, magnesium, zinc, and copper were less likely to die. However, that relationship only held for nutrient intake from food consumption.
People who reported taking more than 1,000 milligrams of calcium per day were more likely to die of cancer. There was also evidence that people who took supplemental vitamin D at a dose exceeding 10 micrograms (400 IU) per day without a vitamin D deficiency were more likely to die from cancer.
It’s worth noting that the researchers did initially see an association between the use of dietary supplements and a lower risk of death due to all causes. However, those associations vanished when they accounted for other potentially confounding factors.
For example, study participants who reported taking dietary supplements generally had a higher level of education and income. They also tended to enjoy a healthier lifestyle. They ate more nutritious food, were less likely to smoke or drink alcohol, and exercised more. So, it appears that people who take dietary supplements are likely to live a longer and healthier life for reasons that are unrelated to their supplement use.
While the study has some limitations, including the difficulty in distinguishing association from causation, and a reliance on self-reported data, its findings suggest that the regular use of dietary supplements should not be recommended for the general U.S. population. Of course, this doesn’t rule out the possibility that certain subgroups of people, including perhaps those following certain special diets or with known nutritional deficiencies, may benefit.
These findings serve up a reminder that dietary supplements are no substitute for other evidence-based approaches to health maintenance and eating nutritious food. Right now, the best way to live a long and healthy life is to follow the good advice offered by the rigorous and highly objective reviews provided by the U.S. Preventive Services Task Force [3]. Those tend to align with what I hope your parents offered: eat a balanced diet, including plenty of fruits, veggies, and healthy sources of calcium and protein. Don’t smoke. Use alcohol in moderation. Avoid recreational drugs. Get plenty of exercise.
References:
[1] Trends in Dietary Supplement Use Among US Adults From 1999-2012. Kantor ED, Rehm CD, Du M, White E, Giovannucci EL. JAMA. 2016 Oct 11;316(14):1464-1474.
[2] Association among dietary supplement use, nutrient intake, and mortality among U.S. adults. Chen F, Du M, Blumberg JB, Ho Chui KK, Ruan M, Rogers G, Shan Z, Zeng L, Zhang. Ann Intern Med. 2019 Apr 9. [Epub ahead of print].
[3] Vitamin Supplementation to Prevent Cancer and CVD: Preventive Medication. U.S. Preventive Services Task Force, February 2014.
Links:
Office of Dietary Supplements (NIH)
Healthy Eating Plan (National Heart, Lung, and Blood Institute/NIH)
National Health and Nutrition Examination Survey (Centers for Disease Control and Prevention, Atlanta)
U.S. Preventive Services Task Force (Rockville, MD)
Fang Fang Zhang (Tufts University, Boston)
NIH Support: National Institute on Minority Health and Health Disparities
Snapshots of Life: From Arabidopsis to Zinc
Posted on by Dr. Francis Collins
Credit: Suzana Car, Maria Hindt, Tracy Punshon, and Mary Lou Guerinot, Dartmouth College, Hanover, NH
To most people, the plant Arabidopsis thaliana might seem like just another pesky weed. But for plant biologists, this member of the mustard green family is a valuable model for studying a wide array of biological processes—including the patterns of zinc acquisition shown so vividly in the Arabidopsis leaf above. Using synchrotron X-ray fluorescence technology, researchers found zinc concentrations varied considerably even within a single leaf; the lowest levels are marked in blue, next lowest in green, medium in red, and highest in white, concentrated at the base of tiny hairs (trichomes) that extend from the leaf’s surface.
A winner in the Federation of American Societies for Experimental Biology’s 2015 BioArt competition, this micrograph stems from work being conducted by Suzana Car and colleagues in the NIH-funded lab of Mary Lou Guerinot at Dartmouth College, Hanover, NH. The researchers are still trying to figure out exactly what zinc is doing at the various locations within Arabidopsis, as well as whether zinc concentrations are constant or variable. What is well known is that zinc is an essential micronutrient for human health, with more than 300 enzymes dependent on this mineral to catalyze chemical reactions within our bodies.
