Possible reasons for the loss of smell and taste

Losing your sense of smell, known medically as anosmia, is much more common than pure loss of taste. But this can affect your taste, too, because the two senses are so closely linked. Around half of people aged 65 to 80 and about three-quarters of those over 80 have some loss of smell, probably due to loss of smell receptors or nerve endings in the nose.

• Yet, some 80-year-olds perform just as well as young adults on smell tests.
• Women often fare better than men — at all ages they tend to have greater sensitivity to smell.
• Because taste bud cells can be replaced, even in old age, people with complete anosmia can usually still distinguish salty, sweet, bitter and sour tastes on the tongue.
• The problem is usually distinguishing between more subtle tastes — which can affect enjoyment of food — and could be one reason that older people may complain that foods do not taste as good as they once did.

• Not surprisingly, people who lose their sensations of smell and taste may become depressed. But the link seems to work the other way around, too — depressed people have reduced taste and smell sensitivity.
• The relationship is complex. For instance, it's hard to know which comes first, as most depressed people have not been tested for sensory disorders before the onset of their illness, and people with sensory disorders are not routinely checked for depression.
• Researchers at Tel Aviv University in Israel studied a group of women and found that those who were depressed also tended to lose their sense of smell. The same researchers also considered the effects of auto-immune disorders such as lupus and rheumatoid arthritis in which auto-antibodies attack the body's own tissues. They believe that the auto-antibodies weaken smell sensitivity and provoke depression, explaining why these symptoms are so common among those affected.
• Scientists at Bristol University in England have also found key chemical changes linked with both depression and taste. Depression is associated with reductions in two brain chemicals called serotonin and noradrenaline.
• As these are also present in taste buds, the researchers reasoned that they could also affect taste sensitivity. They gave volunteers different antidepressant drugs that raise levels of one or the other of these chemicals, and found that increased serotonin levels also improved sensitivity to sweet and bitter tastes, while increased noradrenaline levels improved sensitivity to bitter and sour tastes.
• A placebo drug had no effect on taste sensations. This raises the possibility of using a taste test not just to diagnose depression, but also to work out which brain chemical is affected and so determine which drug might work best in treatment.