Prof Rihmer started his presentation with a look at the effects of a number of environmental and geographical factors on suicide rates.

First up, the geographic effects – suicide rates are higher at higher latitudes (this relationship is significant on both hemispheres) and in the Western United States and Eastern Europe.

Suicide rates are also higher at higher altitude, an effect that was seen from an analysis of all 2,584 counties in the United States. Prof Rihmer explained that this may be due to the very mild hypoxia that comes with higher altitude. Altitude is likely to also explain the longitudinal effect within the United States, as the Western side of the country has a higher mean altitude due to the Rockies.

Interestingly, hypoxia isn’t likely to be the only reason for higher suicide rates at altitude. Higher lithium levels in drinking water have been shown to have a protective effect against suicide, and water supplies at higher altitudes tend to have lower mean levels of lithium. The reason for this is that low levels of lithium have a small, but significant, link to hypothyroidism, which has also been associated with suicide risk.

Summertime sadness

The geographic variances in suicide rates were the appetiser, but now we were ready for the main course – the role of seasonality in suicide.

It’s common knowledge that suicide rates are highest around Christmas. And every November, Prof Rihmer receives calls from journalists looking for a quote for their Christmas suicide story.

So it was a shock to this correspondent, and to many others in the room, when Prof Rihmer (with a grin on his face) told us the month with the actual highest suicide rate… July! After that fact had sunk in, Prof Rihmer unpacked the surprisingly complex explanation for why this is.

Step into the light

Sunshine has a protective effect against suicide and is associated with more hyperthymic temperaments, which explains why suicide rates rise with increasing latitude (where there is a reduction in hours of sunshine). On the other side of the coin, the lack of light that comes with winter is associated with higher levels of depression and melancholy.

However, like in bipolar I disorder, the most dangerous time for suicide is not necessarily when the patient is suffering purely from depression, but during a period of mixed symptoms, when the negativity of depression is combined with the impulsivity of mania.

Similarly, spring/early summer is the most dangerous time of year because the sudden increase in light levels after a long period of darkness causes the brain to release dopamine. Unfortunately, the increase in mood associated with dopamine takes longer to appear than the increase in energy, creating a ‘mixed’ period of low mood and elevated impulsivity, resulting in this seasonal spike in suicide rates.

We are illuminated

Of all the presentations this correspondent has attended at this year’s WPA, Prof Rihmer’s was undoubtedly the one that most left me questioning assumptions I had once taken for granted.

We have heard over and over at WPA that some of the most dangerous times for bipolar patients, and the time their treatment needs the most careful consideration, is during ‘mixed’ periods. And yet it never occurred to this correspondent that external phenomena such as the seasons could drive an emotional response that was just as dangerous.

Prof Rihmer’s presentation was the final one for this correspondent, so it seems appropriate that he left me with the same feelings that the whole of WPA has – excitement to find out more, awareness of how little we truly know, and admiration for the men and women who are shining a light into the great unknown.

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