The smell of ageing

Another year older.  And, according to the bulk of research on aging and our senses of taste and smell, another year closer to permanent decline. Studies on this topic are more or less unanimous, particular with respect to our sense of smell. Across the range of different “scratch and sniff” odours evaluated by 1.5 million people in the National Geographic Smell Survey [1], both odour detection and identification ability declined noticeably after the age of 70. This finding is supported now by very many studies showing that the ability to detect, discriminate, or identify smells progressively declines once we enter our eighth decade. Those odours or flavours that we can detect or identify are, unfortunately, weaker than they once were.

This is a modern malady for a variety of reasons. Enjoyment of food is increasingly an important part of our lives. And in affluent countries, we have started to take it for granted that – barring especially unfortunate genes, particularly foolhardy behavior, or rogue buses – we will of course live well into our 70s and perhaps 80s. Moreover, those staring with most interest (and most denial) at these decades, namely the baby-boomers, expect that a life of good food and wine will continue unabated until the moment that their life-support is switched off. What none of us really anticipate is that our diets will increasingly become blander and foods less distinctive as we ‘mature’.

The food industry has, from time to time, toyed with the notion of producing particular products for elderly consumers. No doubt that this is in recognition of the importance that our sense of smell plays in food appreciation. While this might be a technologically achievable, the marketing issues would be formidable. However, attempts have been made to improve food palatability for elderly in institutionalized care such as nursing homes. Such groups are highly vulnerable to malnutrition, at least partly because as our sense of smell declines, food flavours tend to become less appetizing, and eating less enjoyable. While for many of us, weight gain is the key dietary issue, institutionalized elderly risk serious health problems from under-eating. Because declining health takes a strong psychological as well as physical toll, loss of enjoyment from food can undermine motivations to eat and lead to even poorer health [2]. Attempts to overcome this problem have focused on boosting the taste profile of food, since taste is more robust in the face of increasing age than smell. Flavour ‘amplification’ of food using enhancers such as nucleotides or glutamate has been found to improve both the enjoyment of food and nutritional status in elderly patients [3].

Attempts to understand the causes of age-related olfactory loss have had to deal with the complexity of aging. While age-related changes at all levels of the olfactory system, and indeed the brain itself, have been demonstrated, it is not clear what the causes of these changes might be. Neurological changes to the olfactory system may occur as part of the normal aging process in the same way as changes to the elasticity of our skin. In addition, however, accumulated exposure to industrial chemical or pollutants or tobacco smoke over the adult lifespan might also be a specific factor in smell loss. To further complicate matters, very many diseases are much more common as we age. As a consequence, our intake of medications – some of which are known to have an impact on the sense of smell – increases considerably. Finally, let’s consider the fact that, even in the absence of dementia, cognitive abilities such as attention and memory are also concurrently declining. This means that any test of olfactory identification, for example, must take account of a general reduction in our ability to identify anything at all.

This depressing scenario is relieved a little if you are a woman by the fact that you will not only tend to live longer, but that the decline in the sense of smell will on average be less severe. However, even for men, there’s hope. While the average decline in sense of smell after age 70 looks bad, the variability around this average starts to increase dramatically at this point (see, for example [4]). In other words, the average value itself increasingly becomes unrepresentative of any single individual. So, perhaps because of a history of exposure to something that is very detrimental to smelling, you could be very unlucky and have little ability to smell any longer. On the other hand, the amount of olfactory decline you experience might actually be quite modest.

The key issue then becomes tracking down those factors that protect or harm our sense of smell during our lifetime.  Importantly, the sense of smell is not isolated from other physical and cognitive functions. Variability in smelling mirrors more general variation in functioning in aging. We have all encountered, personally or via media, examples of individuals in their 80s or 90s who seem remarkably healthy, cognitively intact and physically or intellectually productive for their age (see, for example an articulate Bertrand Russell being interviewed at the age of 87; www.youtube.com/watch?v=1bZv3pSaLtY). These individuals are often identified as having “successfully aged”. In contrast, while examples of 90-year-old smokers or heavy drinkers can always be found, it is well established that such behaviours diminish our chances of living to a ripe, or at least healthy, old age.

Recent research by Nordin and colleagues [5] raise the possibility that general health may also be crucial in maintaining a functioning olfactory system. They addressed the question of whether aging per se is responsible for olfactory loss by recruiting a group in their 70s and 80s that were medication-free, cognitively intact and absent serious health problems, industrial chemical exposure or family history of dementia. Compared with a group of university students in their 20s, the elderly group performed equivalently in a threshold task in which they were required to detect the odour of pyridine. This suggests that odour sensitivity reflects overall general physical and cognitive health.

This study does not, of course, rule out other types of olfactory deficits in similarly healthy elderly. But it does suggest the possibility that declining smell might prove to be a manifestation of those same risk factors that are important in overall health as we age. Some fortunate (probably non-smoking) baby boomers might still be enjoying their last sip of Chardonnay as they expire after all.

                                                                                                                       

1.         Gilbert, A.N. and C.J. Wysocki, The Smell Survey Results. National Geographic, 1987(October): p. 514-525.

2.         Wylie, K. and M. Nebauer, The food here is tasteless! Food taste or tasteless food? Chemosensory loss and the politics of under-nutrition. Collegian, Journal of the Royal College of Nursing Australia, 2011. 18: p. 27-35.

3.         Schiffman, S.S. and Z.S. Warwick, Use of flavour amplified foods to improve nutritional status in elderly persons, in Nutrition and Chemical Senses in Aging: Recent Advances and Current Research Needs (Annals of the New York Academy of Sciences Vol. 561), C. Murphy, W.S. Cain, and D.M. Hegsted, Editors. 1989, The New York Academy of Sciences: New York. p. 267-276.

4.         Doty, R.L., et al., Smell indentification ability: Changes with age. Science, 1984. 226: p. 1441-1443.

5.         Nordin, S., O. Almkvist, and B. Berglund, Is Loss in Odor Sensitivity Inevitable to the Aging Individual? A Study of “Successfully Aged” Elderly. Chemosens Percept, 2012. 5(2): p. 188-196.

Le topic du jour: Gout qui importe

In the two or so decades that the so-called French paradox has been discussed widely [1], a variety of explanations for the lower rates of heart disease in France and some other Mediterranean countries have been examined. Yes, consuming wine (and probably specifically red wine) does offer some protection. Beyond that, at least outside of academic epidemiology, it seems a little hazy. The paradox in popular accounts has also come to encompass obesity. Look at all that rich food they eat! Those cheeses! Creamy desserts! It’s amazing that the French aren’t popping the buttons on their Chanel suits!

 As a current visitor to a research institute in the lovely medieval town of Dijon, I have been experiencing my own French food paradox. Eating lunch at the lab canteen is a daily ritual in which an entrée, main course and most often dessert and yoghurt are consumed. My colleagues here reliably inform me that the evening meal is somewhat similar in structure, except that an additional cheese course is always included. Wine is a regular feature of the evening meal if not lunch. Back at home, I would be anxious that this sort of regular intake would permanently double my already ample frame. Perhaps it's the change of scene but after a couple of weeks here, this is starting to seem normal. Certainly, from a weight perspective, none of my colleagues have to worry. But, why not?

 In terms of sensory palatability, the food consumed is neither boring nor lacking in those ingredients that tend to make us worry, especially fat and sugar (although the canteen’s main strength is probably its low prices). My colleagues and I are not eating lettuce leaves and celery, and the (evening) wine is definitely not low alcohol. What does this tell us about those in the US, Britain, Australia and elsewhere desperately trying to control their weight by eating rye crackers and low fat cheese for lunch? The most obvious answer, discussed often previously, is that the French eat smaller portions during meals than we would. If that seems an easy solution, then there is also the fact that eating for the French is a mealtime activity that you undertake in company, and snacking between meals is relatively rare.

 But these two phenomena create their own little paradox. If you eat less food, won’t you be hungry before the next meal and inclined to want to snack? Perhaps, but we know that so-called between meal hunger has, most of the time, little to do with the body demanding required nutrients. It is about habit and the search for pleasure from food.

 And then there’s the question of the healthiness of the food. The obesity ‘epidemics’ in Western countries have led to worries about the energy content of individual foods. While I would argue that the issue ought to be about diet rather than ingredients, there is a popular belief that obesity can be beaten if only delicious foods can be reduced in fat and sugar, and that notion generally supports an underlying attitude that delicious foods are commonly intrinsically unhealthy. Hence, surveys in the USA show that Americans tend to worry a lot about food and its health consequences.

 What about the French – don’t they worry about food and health? The answer seems to be no, or at least not in the way that many other nationalities do. Their focus seems to be much more on the pleasure afforded by food [2]. If you don’t need to worry too much whether the food you eat satisfies your need for pleasure, then you can clearly let your body tell you when you have had enough, and this is what the French appear to do [3].

 Most importantly, the French do not have to worry excessively about whether to eat either healthy food or delicious food, a major concern for American consumers. A recent study has shown that, in contrast to Americans, the French see no conflict between food pleasure and health. Werle and colleagues [4] used the Implicit Association Test (IAT) as of way of determining how closely related the concepts of healthy/unhealthy were to tasty/untasty for male and female French undergraduate students. The advantage of the IAT is that it requires no overt statement from participants about these relationships. Instead, it relies on comparisons of the speeds to respond to different combinations of the concepts being investigated. Using both pictures and words presented on a screen, items reflecting tastiness could be paired with different key presses for healthy and unhealthy (and the same for untasty). For example, a strong association in the participant’s mind between tasty and unhealthy would mean that such key presses should be faster than for tasty and healthy. In other words, congruent concepts when tied to the same response (key press) are responded to more quickly that incongruent concepts.

 These researchers found no difference in the meaning of unhealthy foods; as in the USA, the French idea of unhealthy food involves fat and sugars. However, their IAT results revealed that French participants were faster to respond to a combination of healthy and tasty than they were to healthy and untasty. In a second study, as a direct test of these results, they provided a novel milk-based fruit juice, labeled as either “generally considered healthy” or “generally considered unhealthy”. Consistent with the first study’s conclusions, those participants in the healthy label condition rated the drink as tastier than did the participants in the unhealthy label group.

 What are the origins of the contrasting views of tastiness and healthiness between French and American consumers? Paul Rozin, and more recently Oakes [5], have shown that many American consumers have adopted very simplistic approaches to categorizing foods. In the consumer mind, foods are broadly either good (healthy) or bad (unhealthy) and this distinction is typically made in terms of fat content. To a large extent, this results from long-stranding government and media-based emphases on fat intake as the major cause of both obesity and heart disease. From the consumer’s perspective, adopting undemanding rules about foods is understandable given the potential complexity of nutritional information, but may have unforeseen consequences, beyond simply a guarantee of boring mealtimes.

 Putting foods into good and bad baskets may also be counterproductive in attempts to loose weight. Thus, the notion of tasty = unhealthy = fat is sufficiently ingrained in the USA that consumers can ignore the potentially greater weight gain from a higher calorie “good food” if it is contrasted with an obviously fat containing, but lower calorie “bad food”. One study of US college students who were given cookies to eat reveals where this can lead. The researchers assigned the students to receive information about the healthiness of the cookies. Those students who were told that the cookies were a ‘healthy snack’ ate 35% more than did those told that they were unhealthy [6]. Dieting never tasted so good!

 The link between dieting and equating tastiness with unhealthiness is even evident among the French participants in the Werle et al. study. There, the strength of the association between healthy and tasty was found to be weaker for highly restrained eaters (that is, those who try to consciously restrict their food intake) than for less restrained eaters. It is not clear in which direction(s) the arrow of causation points here, but such a finding does make us wonder whether the process of food restriction acts to distort attitudes towards foods and health.

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1.  Dolnick, E., Beyond the French paradox. Health, 1992. 6(6): p. 40-49.

2.  Rozin, P., Food is fundamental, fun, frigtening, and far-reaching. Soc. Res., 1999. 66: p. 9-30.

3.  Wansink, B., C.R. Payne, and P. Chandon, Internal and External Cues of Meal Cessation: The French Paradox Redux? Obesity, 2007. 15(2): p. 2920-2924.

4.  Werle, C.O.C., O. Trendel, and G. Ardito, Unhealthy food is not tastier for everybody: The ‘‘healthy = tasty’’ French intuition. Food Qual Pref, 2013. 28: p. 116-121.

5.  Oakes, M.E., Beauty or beast: Does stereotypical thinking about foods contribute to overeating? Food Qual Pref, 2005. 16: p. 447-454.

6. Provencher, V., J. Polivy, and C.P. Herman, Perceived healthiness of food. If it’s healthy, you can eat more! Appetite, 2009. 52: p. 340-344.