Sense of smell 'may predict lifespan' | Hacker News Reader

Sense of smell 'may predict lifespan'

bbc.com

46 pointssuprgeek22 comments

Aging is a global phenomenon of damage accumulation throughout the body: more damage means faster aging. People who show more damage in any one measure tend to show more damage in all the others too, as it all stems from a few root causes. This bears up in epidemiological studies, but there is a fair amount of individual variation.

Almost every decline in aging that can be measured can be correlated with near future mortality. Grip strength and walking speed are the common ones presently used, and finding others should be in no way surprising.

Agreed.

Also, these types of studies always claim to have corrected for differences in confounding variables, but there are always more confounding variables than have been corrected for, and all they end up doing is a statistical comparison of data with a fewer but still significant number confounding variables, and if the sample size is big enough they will find a significant P value and try to imply some sort of causation/significant correlation.

I like how the article succinctly discussed different possible causal mechanisms for losing a sense of smell that an individual formerly had as a marker for declining health and impending death.

This is especially interesting in view of the reduction of sense of smell over millions of years in the ancestral line of human beings. Before animals in the clade Primates developed trichromatic color vision, they distinguished fruits ripe enough to eat from fruits that were not mostly by smell. But after color vision improved, there was no longer selection pressure to maintain the sense of smell genes that gave the same information about food plants, and so random mutations gradually knocked out those genes. Comparative DNA analysis shows that human beings have descendant genes that were once used for accurate sense of many smells that human beings can no longer distinguish, but that sensory capacity was lost by genetic drift until lack of accurate sense of smell for many substances became fixed in the human population. A fascinating book that tells this story in more detail is The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution by Sean Carroll,[1] a very readable and enjoyable book about molecular biology studies and the evidence they provide for biological evolution.

[1] http://www.amazon.com/Making-Fittest-Ultimate-Forensic-Evolu...

Interesting possible correlation. I have a horrible sense of smell. I always have. I can certainly smell some things - and particularly strong scents like coffee, fish, or oranges definitely register, but I'm able to also completely block out offensive odors in a way that I've found others cannot. I've always felt that if I had to suffer from a deficiency in a sense, smell is the one to choose.

The assessment involved identifying distinct odours encased on the tips of felt-tip pens.

They don't discuss range, just accurate identification. I think I have lost some range over the years, but not accuracy. Up close I can identify smells fine.

But sometimes I'll make a cup off coffee, someone will remark how good it smells, and I can't smell it at all until I'm 30cm from the cup.

I think they are talking about a radical change in your sense of smell being a predictor, rather than your overall sense of smell.

Interesting - I don't have a sense of smell (and never have). I don't think I'm at risk of dying from that, however, barring an undetected gas leak.

Loss of sense of smell is fairly serious, though, so this isn't too surprising.

you don't have a sense of smell? How is this called? Do you actually never smell anything or is it just very very weak? Does it also mean that when eating you basically couldn't tell between smoked herrings and cheese other than by level of saltiness/texture?

I hope I am not unpolite in asking and please forgive my curiosity, I've never heard of "congenital olfactive loss" and my mind was just blown.

> you don't have a sense of smell? How is this called?

Anosmia.

http://www.chiark.greenend.org.uk/~sgtatham/smell.html

It's not impolite to ask - I don't mind answering questions about it. "Congenital Anosmia" is the correct term. It's fairly serious when someone loses their sense of smell, and can cause weight loss and depression. It can also be a symptom of some fairly serious conditions (e.g. Parkinson's).

For food - I prefer strong flavors (smoked salmon, capers, onions). Subtle flavors like spices are lost on me - basil, spinach, and mint all taste the same. Cheeses can be strong - I think I could tell the difference between blue cheese and provolone, but I haven't done an experiment. I'll have to try that sometime.

It is possible I have a very week sense of smell. I can kind of smell coffee, and there are a few times I've smelled an orange, but that hasn't been reproducible. My dog got sprayed by a skunk one time, and I couldn't smell that, so I think it's accurate to say I don't have a sense of smell.

I can "smell" things like vinegar and bleach, but I think that's the trigeminal nerve. I can't tell the difference between white vinegar and balsamic vinegar, however.

My mom can't smell either - nor could her dad.

Super interesting.

I've also got no sense of smell, though my ENT thinks it was due to an accident I had as a baby (fell face first onto broken glass), that severed the nerve.

I can smell absolutely nothing (not gas, not coffee, nada)... but, on the other hand, have a really strong sense of taste. Maybe this is what's leaning the doctor to that.

thanks for sharing, that's super interesting. just one question since you mentioned salmon and cheeses: do you get the bacon flavor/smell ??? that's a favorite aroma for a lot of people.

I like bacon, but it's not my favorite food. It's also never triggered what I think of as a smell, like coffee does sometimes, and oranges have done a couple times. So I don't think I'm getting any of the aroma.

thank you very much, yours (and others') replies were very interesting.

A good friend of mine has no sense of smell* - she's always been observed by people to be a picky eater with odd eating habits. Over time it all started to make sense. She clearly organizes things by taste bud taste and doesn't really like mixing flavors, e.g. anything with a sweet component she doesn't like unless it's a dessert, even if it's a subtle sweetness.

She can pick up on various ingredients, but she describes them in ways that are different from most people. For instance, garlic is a 'sweet' flavor to her. As with any lack of sense situation, it's difficult to really discuss with someone as the one person has absolutely no frame of reference, but from observation I've been able to see how things work.

One amusing anecdote was when we went over and she was making a cake. "What's that burning?" we asked. She had taken it out of the oven and put on a burner which was actually on. Well, the bottom half of the cake was burned to a crisp and she had no idea it was happening.

* Well she thought she had 0% sense of smell until one day she was working in a city-wide open sewer pit in a third world country. She said that she detected something unpleasant there that she thinks was a smell. So it would seem that it's really a super-super-super-super poor sense of smell.

I'm the opposite - I'm a very non-picky eater, and always have been. Mixed flavors don't bother me either.

Well, me too. Never have been able to detect odors anywhere near to normal degree. So I'd fail the test for "peppermint, fish, orange, rose and leather" miserably.

FWIW humans rely much less on sense of smell than many other creatures. Interestingly, animals with poorer odor detection tend to have better vision. Raptors have excellent vision and aren't reliant on smell to detect prey.

Human vision is also well-developed, the only trichromats among the great apes.

Goes to show, "tests" don't always apply in each and every instance.

The research looks at loss of smell, not never having a (good) sense of smell as an indicator.

As someone with a history of chronic sinus problems (which were really just the tip of the iceberg -- an indicator of much more serious problems, actually), I can well imagine ...a connection here between deteriorating sense of smell and underlying serious health problems. As my health improves, so does my sense of smell.

I don't feel like I am saying this very well. Let's try this: If someone goes blind or has other significant visual impairments, we typically take that seriously as a big deal and then may look for underlying causes, but the loss of sense of smell tends to not be treated quite the same way.

Interesting that "orange" is one of the smells tested: there are at least 3 smells to an orange – the oil in the peel, the juice, and the rind or pith (the white stuff). Not to speak of the varieties of fish (or do they mean rotting fish??).

So maybe dumb question but did they take into account the age of the participants? That is the older people in the study would tend to has less sense of smell and die sooner.

Yup:

And despite taking issues such as age, nutrition, smoking habits, poverty and overall health into account, researchers found those with the poorest sense of smell were still at greatest risk.

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