Do depressed people get fewer colds?

October 3, 2012 at 5:57 pm | Posted in Uncategorized | 1 Comment
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An interesting paper in Molecular Psychiatry suggests that dim lights at night may be a risk factor for depression.

I can’t help thinking of Ben Goldacre’s comment about the Daily Mail‘s ‘ongoing ontological program to divide all inanimate objects into ones that will either cause or cure cancer‘. Note that the research was done on lady hamsters, and that just because both mood disorders and night-lighting have become far more common over the last half century, that doesn’t prove a causal link between them.

But seriously, if the suggestion holds up in future studies, this is one risk factor we could all do something about, yes?

If only. My local council recently replaced some of the astronomers’ nightmare, orange sodium lighting, with white lights so large and bright that the wildlife’s probably still reeling. Do they switch the lights off at night? Of course not. Safety reasons. The new lights, apparently, cast less uplight (good), but they still flood every bedroom in the neighbourhood. And since only some were changed, my nights are now, like the future, bright and orange, instead of merely orange.

Motion sensors would sort the problem. I guess they’re too expensive.

Milky WayWould being able to see the stars make us all feel better? Now and again I’m lucky enough to get to a part of the UK where I can still, on a clear night, see the Milky Way. (Here, if I get to see the Orion Nebula it’s a good night.) The first time, I looked up at the night sky and couldn’t get my bearings at all. So many stars! It was as if someone had gone on a rampage through De Beers and hurled the diamonds onto a swathe of black velvet. Not orange — as in  where I live — but beautiful, mind-stretching black. (Image from Forest Wander/Creative Commons.)

The link between night light and depression is likely to lie less in our lack of access to anti-narcissistic visions of eternity and infinity, however, than in the immune system, according to this paper’s authors. They think the pro-inflammatory factor TNF-α (tumor necrosis factor alpha) may be involved. Depression has been linked to heart disease and cancer — not exactly a depression-busting statement, that — and inflammation is thought to be the common mechanism: the immune response being too active for too long.

Seasonal affective disorder, of course, is linked to lack of daylight — but that’s natural light, and in the daytime.

Perhaps, if our governments refuse to change the lighting, they’d consider distributing omega-3 fish oils to their photon-bludgeoned constituents. Omega-3 fatty acids are known to have anti-inflammatory effects (the site link is to the IFBB, for whom I’ve done some consultancy work; they’re an independent science charity specialising in research into nutrition, including fatty acids).

Inflammation is also the key in an interesting paper in Molecular Psychiatry from earlier this year, on the PATHOS-D (PAThogen-HOSt-Defense) hypothesis. This is the idea, roughly, that depression is so common and persistent in our species that the genes which deal out that particular unhappy fate must have advantages as well as the obvious disadvantages. (David Horrobin made a similar case for schizophrenia  in The Madness of Adam and Eve.)

The authors, Raison and Miller, suggest that the gene variants which predispose to depression also boost the immune system’s response to infection. By thinking about depression as related to immunity, they argue, its antisocial effects — withdrawal, anhedonia and so on — can be put in a wider context in which they make more sense. Perhaps our bodies don’t always prioritize our social lives (and the bright lights which often go with them) as highly as our culture-driven, media-pressurised minds do, if you’ll forgive the Cartesian metaphor.

In which case, depression may go along with the ability to fight off a cold. I wonder, do bipolar people’s susceptibility to infections vary with their mood? Or are they exposed to less infection when depression strikes, because of the social impact it has? Do people in brightly lit areas get fewer colds than those where the night lights are less bothersome? Imagine how many confounding factors you’d have to take into account to answer those questions!

It’s an interesting field, neuroimmunology. But it’s ever so difficult.


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