Six years ago my brother took his own life. He was 28 years old.

Tragically, suicide is not as rare as one might think. In 2016, the last year global data is available from the World Health Organization (WHO), there were an estimated 793,000 suicide deaths worldwide.Most were men.

In the UK, the male suicide rate is its lowest since 1981 – 15.5 deaths per 100,000. But suicide is still the single biggest killer of men under the age of 45. And a marked gender split remains. For UK women, the rate is a third of men’s: 4.9 suicides per 100,000.

It’s the same in many other countries. Compared to women, men are three times more likely to die by suicide in Australia, 3.5 times more likely in the US and more than four times more likely in Russia and Argentina. WHO’s data show that nearly 40% of countries have more than 15 suicide deaths per 100,000 men; only 1.5% show a rate that high for women.

The trend goes back a long way. "As long as we've been recording it, we've seen this disparity," says psychologist Jill Harkavy-Friedman, vice-president of research for the American Foundation for Suicide Prevention, a health organisation that supports those affected by suicide.

Suicide is a hugely sensitive, complex issue with a tangled multitude of causes – and the very nature of a death by suicide means we can never fully know the reasons behind it.

Still, as mental health awareness has grown, there is greater public understanding about potential contributing factors. One of the questions that has persisted, though, regards this gender gap. It seems especially large given that women tend to have higher rates of depression diagnoses.