"According to the World Health Organisation, depressive disorders were the third biggest global health problem in 2004; by 2030 they will be No 1."
The Times (£), 25 February 2013
Frequently described as debilitating, yet often derided as a disease of the over-indulged, depression is something of a medical conundrum. As a result, some people might be surprised to learn that the World Health Organisation (WHO) has recognised clinical depression as one of the greatest threats to the well-being of the world population.
The Times correctly reported that the WHO's 2008 analysis of global health (based on 2004 statistics) ranked unipolar depressive disorders (major depression) as the third leading 'burden of disease' or DALY (Disability Adjusted Life Year).
The Global Burden of Disease Study, introduced in 1990, estimates the health effects of more than 100 diseases for eight regions of the world. As a metric, it uses the DALY, which is based on "years of life lost from premature death and years of life lived in less than full health".
In order to calculate the years of life lost to a disease we multiply the number of deaths at each age by the global standard life expectancy for that age group. Each disease is also accorded a 'weight factor' that's indicative of its severity, with 0 as a state of 'perfect health' and 1 as death.
This means that the Years Lost to a Disability (YLD) is equal to:
number of incident cases in that period × average duration of the disease × weight factor
So the DALY of depression in 2004 - 65.5 million - shows how many years of life have been lost or lived in less than full health by people the world over who suffer from it.
As the WHO acknowledge, there are relatively few deaths from depression ("direct mortality"), so its high standing in the league table will be more due to years of life 'in less than full health' than actual years of life lost.
A bourgeois affliction?
Helpfully, the WHO calculates a global and a regional DALY for every disease, including depression. As a result, we can see that unipolar depression tops the DALY table for the Americas. The situation is similar in the Western Pacific and Europe (where depression is ranked second and third respectively).
In the equivalent list of DALYs for Africa, depression doesn't even feature. Meanwhile, in the Eastern Mediterranean, depression is only the seventh biggest 'health problem', with respiratory diseases and diarrhoeal infections much more likely to impact upon a person's wellbeing.
Yet this doesn't mean that people in Africa are somehow immune to depression, or that the condition is a disease of the wealthy. As the WHO notes, people living in the Middle East and Africa "also suffer severely from the problems that affect people in high income countries".
As we would expect, fatal diseases dominate the DALY tables for these regions. While HIV/AIDs is responsible for more than 12% of DALYs in Africa, the prevalence of neonatal infections and birth trauma explain the high infant mortality rates that we find in parts of each continent.
It's therefore not particularly surprising that depression, being the cause of relatively few deaths, doesn't feature in a list of Africa's biggest health problems.
All in all, the picture spells out that for both middle and high income countries, where there's likely to be better access to healthcare and where it might be more common to arrive at a mental health diagnosis, depression ranks first.
Will depression be the biggest global health problem by 2030?
The same WHO report suggested that while the number of DALYs would decrease from 1.53 billion in 2004 to 1.36 billion in 2030, depression would top the DALY table in 2030, out-ranking heart disease and road traffic accidents (a health problem that jumps from ninth in the list to third, presumably as a result of increased car ownership).
According to the WHO's projections, "people in all regions of the world will live longer and with lower levels of disability, particularly from infectious, maternal, perinatal and nutritional conditions".
Depression can cause terrible suffering, and some people take their own lives to escape it. However, an increase in the prevalence of depression over the next 15 years might indicate that global health is improving. Or, to put it another way, a disease that causes relatively few deaths will be the world's number one health problem.
Flickr image courtesy of Bert Werk
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