Did you know that more than 1.5 billion people worldwide suffer from hearing loss? But in some cultures, people retain their hearing into old age. Here’s our first story.
In the United States, age-related hearing loss affects about a quarter of those in their 60s, more than half of those in their 70s, and 80 percent of those in their 80s. More than 95 percent of centenarians have been found to have severe hearing loss. Because of impaired communication, this may lead to social isolation, loneliness, and depression. It may even threaten one’s life due to an associated increase in motor vehicle accidents.
What can we do to prevent age-related hearing loss? It’s said to be a natural part of the aging process, but that’s what we used to think about pathological conditions like high blood pressure. The vast majority of people eventually develop hypertension, just like the vast majority of people eventually lose their hearing; so, it must just be an inevitable consequence of growing old, right?
But then it was discovered that there were rural populations living in Africa and Asia that ate and lived healthier, that didn’t experience an inexorable rise in blood pressure as they aged. So, it appeared hypertension was more a lifestyle choice than an aging effect—and the same may be true for hearing loss.
The Mabaan tribe living in the Sudanese desert was found to retain their hearing into old age. Other studies on isolated native populations found that exposure to modern civilization appeared to undercut their hearing advantages. What is it about our modern world that appears to be leading to a loss of hearing as we grow older?
Age-related hearing loss is a result of the premature death of the sensory hair cells in our inner ear which turn vibrations to electric signals to the brain. Once they’re lost they don’t grow back; so, prevention is critical. The question is: What is killing them? A study of more than 2,000 twins found that the heritability of age-related hearing impairment was only 25 percent; so, most of risk is due to nongenetic influences.
Risk factors include repeated exposure to loud noises, smoking, and ototoxic (or hearing-damaging) medications. Noise exposure early in life appears to render the inner ear more vulnerable to aging. Animal studies suggest exposure to low level but constant noise over 60 decibels may also be harmful. This has not been demonstrated in humans, but if you use a white noise generator to sleep, it can’t hurt to check that it’s under 50. Medications known to be ototoxic include aminoglycoside antibiotics (like streptomycin, amikacin, neomycin, and kanamycin), which are among the highest-risk medications for hair cell toxicity. But NSAIDS, anti-inflammatory drugs like aspirin, ibuprofen, and naproxen, and loop diuretics (for example, furosemide sold as Lasix) have also been linked to progressive hearing loss. However, the key to the preservation of old-age-hearing of the Mabaan tribe may be their diet.
The reason the Mabaan researchers concluded that their diet likely accounted for their lack of age-related hearing loss is because they also appeared to lack something else: coronary artery disease. What kills more of us in the industrialized world than anything else doesn’t appear to touch them at all. Their blood pressures are also perfect their whole lives, at about 110 over 70 into their 70s, while we, on average, become hypertensive, exceeding 130/80, starting in our 40s.
And no wonder—their diet is “almost free of animal protein” and centered around whole grains (sorghum). So, they suggested, in addition to the absence of loud noise, that atherosclerosis clogging the small blood vessels feeding their inner ears may be the underlying cause of age-related hearing loss in most of the rest of the world. But you don’t know until you put it to the test, which I’ll cover next, after dealing with a supplement shown to slow age-related hearing loss.
Healthier diets are associated with a significantly lower risk of hearing loss, and for all three diet quality scoring systems these researchers used, avoidance of meat was most strongly associated with lower risk. The Mabaan who preserved their hearing into old age, ate little meat, but also weren’t eating sugary junk––explaining their almost total absence of dental cavities. A high glycemic diet of refined carbs is also associated with developing age-related hearing loss. If it’s the blood sugar spikes, that would explain why diabetics and prediabetics are also at higher risk. Even among whole grains, sorghum, which is the center of the Mabaan diet, has a particularly low glycemic index due to its resistant starch content, causing about a 25 percent lower rise in blood sugar compared to whole wheat.
Impaired blood circulation may also explain how noise damages the inner ear, as loud noises cause constriction of the accompanying blood vessels. This may also help clarify the link between obesity and hearing loss. Excess weight may just be a proxy for unhealthier diets, but the pro-inflammatory state of obesity can itself lead to vascular dysfunction. Measures of systemic inflammation seem to directly correlate with age-related hearing loss, as do measures of oxidative stress.
In my video on brain inflammation, I introduced the antioxidant defense activator Nrf2, called “guardian of healthspan and gatekeeper of species longevity.” Those born with a genetic variant Nrf2 that doesn’t encode as well are significantly more likely to develop impaired hearing, implicating the role of free radicals in the process of hearing loss. You can look in the back of people’s eyes and measure the amount of macular pigment—the lutein and zeaxanthin antioxidants concentrated in greens—and correlate that with superior hearing.
The population data on antioxidant intake and hearing loss are mixed, though. Take vitamin C, for example. Some studies show that higher vitamin C intake is associated with better hearing, but others failed to find any significant connection. The only way to tell if antioxidants help or not—you know the drill—is to put them to the test.
Adding antioxidants to the diets of rats seems to help prevent age-related rat hearing loss, but doing the same thing in mice doesn’t appear to help. The most exciting preclinical data may be a study in which aged rats randomized to added blueberries looked like they had a reversal in hearing deficits–in fact, ending up better than the young rats. Wait, I thought hair cells don’t regenerate?
Our ability to hear doesn’t just have to do with our ears, but our brain. As we age, our auditory cortex in the temporal lobe of our brain loses some of its ability to discriminate and understand speech, even in a quiet environment. We don’t just need to sense sounds, but make sense out of them. That’s where blueberries seemed to come in, reversing the age-related cognitive deficits in auditory processing. But what about in people?
There are studies lacking control groups that documented improvements in hearing loss, giving people antioxidant supplements like vitamins A, E, C, and alpha-lipoic acid. But when properly put to the test in a randomized, double-blind, placebo-controlled trial of a whole list of antioxidants, the supplements flopped—no effect on any of the measured hearing aspects. Is there any supplement that has been shown to help with hearing in older adults? Yes, folic acid, the supplement form of folate, found concentrated in beans and greens.
Some observational studies had found that higher levels of folate in the blood seem to correlate with better hearing, but maybe that’s just a marker of eating a healthier diet in general. So, Dutch researchers set out on an ambitious three-year double-blind, placebo-controlled trial randomizing more than 700 older men and women to take 800 μg of folic acid a day or an indistinguishable placebo. Excitingly, those who had been taking the folic acid suffered significantly less decline in hearing at speech frequencies. The effect size was rather small, such that one might expect the proportion of men, for example, who would be hearing aid candidates at age 75 might drop from 33 percent to 22 percent with folic acid supplementation. Also note the study was done in the Netherlands, where, at the time, the food supply was not fortified with folic acid. In the U.S., where folic acid fortification has been mandated in refined grain products for decades, it’s unclear how much additional benefit supplements might add. Regardless, the healthiest sources are dark green leafy vegetables and legumes. (A cup of cooked lentils has 90 percent of adult daily needs.)
Finally, today, we hear about the results of a diet that may slow or even reverse hearing loss.
A 2021 scoping review on the role of nutrition in the development and prevention of age-related hearing loss screened thousands of papers and concluded: “Diets rich in saturated fats and cholesterol have deleterious effects on hearing that could be prevented by lower consumption.” The case of the Mabaan I noted before makes for a compelling story, but on what exactly are they basing their conclusion? It’s true that in laboratory animals you can prove it. Randomize rats to added saturated fat or chinchillas to added dietary cholesterol, and scientists can show atherosclerosis-inducing diets exacerbate inner ear damage and hearing loss, even without noise exposure. But that doesn’t necessarily mean the same is true in people.
There is cogent epidemiological data. For example, a study of thousands of twins was able to draw a significant link between a high cholesterol diet and hearing impairment. In the Blue Mountains Hearing Study, which enrolled thousands of older men and women to study age-related hearing loss, dietary cholesterol was the nutrient component most associated with hearing loss. Those eating about two eggs worth of cholesterol a day had 34 percent greater odds of hearing loss compared to those only getting about a single egg’s worth. Consistent with a vascular cause, those on statins, and particularly those at higher doses, appeared to be at lower risk. The researchers suggest that high cholesterol intake may interfere with the circulation within the inner ear itself, or atherosclerotic inflammatory changes could reduce blood flow to the tiny arteries feeding the inner ear. But how about looking inside the arteries to see if this is actually true?
The extent and severity of coronary artery disease in the heart, as determined by angiogram, was found to closely correlate to hearing loss. Since atherosclerosis is a systemic disease affecting the entire arterial tree, this has relevance for the arteries feeding the inner ear. The same was found for the amount of atherosclerotic plaque found in the carotid arteries in the neck. The greater the plaque, the poorer the hearing, and the more plaque they found, the greater risk of further hearing impairment measured over the subsequent five years. Getting closer, but how about the arteries that directly supply the inner ear? Early autopsy data suggested sclerotic changes in the blood vessels of older ears contribute to inner ear degeneration, and these days, direct imaging studies correlate the degree of hearing loss with atherosclerotic narrowing of those inner ear arteries.
Now, all we need is an interventional trial to wrap it all up in a bow. Yes, high-cholesterol and high saturated fat diets have been shown to kill off those critical inner ear cells and cause hearing loss in lab animals, but it’s not like you can lock hundreds of people up for a few years and force them to eat different amounts of saturated fat and see what happens to their hearing. Oh, but you can, and they did: The Finnish Mental Hospital Study.
In 1960, one of two mental hospitals near Helsinki had their menus changed to decrease their intake of saturated animal fat. Then, after a few years, the two hospitals switched their menus over. It was one of the first interventional trials of its kind suggesting that you could decrease heart disease deaths by decreasing saturated fat intake. Ah, but what happened to their hearing? It followed the exact same pattern. As their heart disease got worse, so did their hearing. And then when the hospitals switched, the reverse happened. And not just by a little. Those in their 50s in the lower saturated fat hospital ended up with significantly better hearing than the group in the control hospital that was ten years younger. The researchers concluded: “our audiological studies lead us to conclude that diet is an important factor in the prevention of hearing loss.”
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