There's quite a bit of evidence now that socializing — having frequent contact with others — helps protect against cognitive impairment in old age. We also know that depression is a risk factor for cognitive impairment and dementia. There have been hints that loneliness might also be a risk factor. But here’s the question: is it being alone, or feeling lonely, that is the danger?

A large Dutch study, following 2173 older adults for three years, suggests that it is the feeling of loneliness that is the main problem.

At the start of the study, some 46% of the participants were living alone, and some 50% were no longer or never married (presumably the discrepancy is because many older adults have a spouse in a care facility). Some 73% said they had no social support, while 20% reported feelings of loneliness.

Those who lived alone were significantly more likely to develop dementia over the three year study period (9.3% compared with 5.6% of those who lived with others). The unmarried were also significantly more likely to develop dementia (9.2% vs 5.3%).

On the other hand, among those without social support, 5.6% developed dementia compared with 11.4% with social support! This seems to contradict everything we know, not to mention the other results of the study, but the answer presumably lies in what is meant by ‘social support’. Social support was assessed by the question: Do you get help from family, neighbours or home support? It doesn’t ask the question of whether help would be there if they needed it. So this is not a question of social networks, but more one of how much you need help. This interpretation is supported by the finding that those receiving social support had more health problems.

So, although the researchers originally counted this question as part of the measure of social isolation, it is clearly a poor reflection of it. Effectively, then, that leaves cohabitation and marriage as the only indices of social isolation, which is obviously inadequate.

However, we still have the interesting question re loneliness. The study found that 13.4% of those who said they felt lonely developed dementia compared with 5.7% of those who didn’t feel this way. This is a greater difference than that found with the ‘socially isolated’ (as measured!). Moreover, once other risk factors, such as age, education, and other health factors, were accounted for, the association between living alone and dementia disappeared, while the association with feelings of loneliness remained.

Of course, this still doesn’t tell us what the association is! It may be that feelings of loneliness simply reflect cognitive changes that precede Alzheimer’s, but it may be that the feelings themselves are decreasing cognitive and social activity. It may also be that those who are prone to such feelings have personality traits that are in themselves risk factors for cognitive impairment.

I would like to see another large study using better metrics of social isolation, but, still, the study is interesting for its distinction between being alone and feeling lonely, and its suggestion that it is the subjective feeling that is more important.

This is not to say there is no value in having people around! For a start, as discussed, the measures of social isolation are clearly inadequate. Moreover, other people play an important role in helping with health issues, which in turn greatly impact cognitive decline.

Although there was a small effect of depression, the relationship between feeling lonely and dementia remained after this was accounted for, indicating that this is a separate factor (on the other hand feelings of loneliness were a risk factor for depression).

A decrease in cognitive score (MMSE) was also significantly greater for those experiencing feelings of loneliness, suggesting that this is also a factor in age-related cognitive decline.

The point is not so much that loneliness is more detrimental than being alone, but that loneliness in itself is a risk factor for cognitive decline and dementia. This suggests that we should develop a better understanding of loneliness, how to identify the vulnerable, and how to help them.