March 29, 2017
Our sense of taste is a lot more integral to our lives than we probably realize sometimes. It's at the center of every birthday party when we bite into a cake, at our meetings when we sip coffee, and complements our Netflix binges when the takeout finally comes knockin' at the door.
But what happens to that comforting sense of taste as we get older? Are we really losing our sensitivity as we age?
Curious to know more, we reached out to Beverly Cowart, a scientist at the Monell Chemical Senses Center and adjunct professor at Jefferson Health, for an answer.
Do our taste buds actually dull as we age?
The first thing you need to understand is the difference between taste and smell. Because both contribute to food flavor, which is usually what people use taste to refer to. Taste buds only mediate sweet, sour, salty, bitter and savory flavors. Most of the rest of the flavor of food is mediated through the olfactory system. As you chew and swallow food, molecules are released in the mouth and flow up the back of the throat to the nose and stimulate smell receptors. And your brain puts info from both systems together, so it's perceived as kind of a uniform quality. But the difference between strawberry and cherry, the various herb flavors, chocolate and vanilla, it's primarily an olfactory difference. So the taste system does decline somewhat with age, but not very much. The olfactory system does decline substantially with age, particularly in men. And when people begin to lose their smell they lose a lot of the flavor of food and tend to describe it as "tasteless."
So it's more true to say we lose our sense of smell than taste?
Right. But that does have an impact on food flavor.
Why do you think that's not more common knowledge?
It's because when your brain receives information from the olfactory system and taste system, it integrates them in an area of the brain that is actually the primary [gustatory] cortex. So some of the smell signals get sent over to the taste area. I think it's because of that, that almost all of what we refer to as the taste of food, it's all referred to in the oral cavity. People perceive it as coming from our mouth. That's a source of the confusion.
You mentioned that men experience loss more than women? Why?
We don't really know. In fact, all the studies that have been done in large populations have been cross-sectional studies. Some of it could be that older men have had more exposure to chemicals and to things that can damage them from the environment than women, particularly because of occupational differences in the older cohort. So, that may contribute to it. It could also be, the olfactory system and taste system as well, they both depend on turnover of their receptor elements.
So, because those receptors are there to protect chemicals and chemicals can sometimes be damaging, in the taste system, the receptor elements are [turned over pretty quickly]. In the olfactory system, the receptor elements are primary neurons. They're one of the few types of neurons in the body that do regenerate throughout the lifespan, but it's a very complicated process. When an olfactory receptory neuron dies, and a new one grows to replace it, the nasal cell has to mature into a neuron and then go into the brain, and that process slows down with age and may be more volatile to that slowing down...
With the taste system, is there a certain number of taste buds we're born with?
No, there are more individual differences than that. And the things that people are sensitive to, there are genetic determinants. Some people are susceptible to various bitters than others, and that simply has a genetic basis in terms of the types of receptors they express. But there is a lot of redundancy in the taste system, which is one of the reasons it probably doesn't show as much decline with age as smell does. It perceives a lot fewer qualities and you can perceive the basic tastes really everywhere there are taste buds on the tongue and throat -- it actually has three different cranial nerves that carry taste info. So, you can knock out a portion, one quadrant of your tongue, and not really notice there's been a change. Smell has only got one cranial nerve devoted to it: the olfactory nerve. And that nerve, those nerves connect directly to the brain...and are volatile to damage if you have a head injury.
Is there a good way to protect our sense of taste as we age?
Well, to the extent that you're probably better off living in a clean environment. There is data suggesting people who live in polluted areas like Mexico City have earlier losses than people in clean environments. But this relates to the olfactory system – I'm talking primarily about olfaction and flavor and not food taste as a flexible system. And there's increasing evidence through a number of sources that using sense of smell can strengthen it. Just paying attention to odors, trying to label them. It seems to be able to both refine your ability to perceive them sensually and even stimulate receptor turnover.
Anything to add?
I guess the only other thing I would mention, is we've talked about aging as general issues in terms of losing the sense of smell. Another thing that tends to happen more often to older women, and can be a real surprise to them, is sometimes a simple cold can lead to a relatively sudden onset of smell loss that -- sometimes the losses from viral infections will gradually return, but they don't always. They can be permanent. It's something that's important to go see a physician about as soon as you notice it and start working to stimulate regrowth early.
