NEW THINKING ON MENTAL WELLBEING MAY OPEN UP GREATER SCOPE FOR HEALING, ONE SMALL CHANGE AT A TIME
ONE OF THE curious factors in human evolutionary history is how often a genetic advantage can swing back as a sword. A sensitive immune system helped human survival by blanket-bombing foreign microbes, a huge benefit in our early history. But now, with fewer cuts and wounds to address, it can trigger autoimmune diseases. Anxiety was another trait that assisted humans to become the most successful species. Instead of lolling around the savannah waiting for the breadfruit to drop, humans — concerned about famine — were pre-emptively planting, tending and driving off competitors to significant advantage. But this anxious gene has also become a problem.
Most New Zealand families have at least one member coping with depression or anxiety, conditions that can take a terrible toll on a sufferer’s life and on those close to them. The cost to the financial health of a country is also significant. A 2015 British study found that the economic consequences of depression and related disorders were so enormous that completely curing depression would add four per cent to the British GDP, tripling the projected annual growth rate. New Zealand figures are thought to be roughly proportional.
It’s an international problem; by 2030, depression is predicted to be the most significant single cause of disability in the world. In Japan, depression is referred to as “kokoro no kaze”, which means “a cold of the soul”. In Sweden, a country often cited as suffering from seasonal affective disorder (SADS), the gloomy Soren Kierkegaard wrote: “The exact nature of despair is that it does not recognize despair.”
Depression runs in families. The background risk of depression in the general population is about one in four — everyone has a 25 per cent chance of becoming depressed at some point in their lives. And if a parent has been depressed, the risk jumps by a factor of three. But is it nature or nurture, genetics or environment?
Research proves that pairs of identical twins, with 100 per cent identical DNA, are more likely to have similar experiences of depression than pairs of non-identical twins, with 50 per cent identical DNA. Depression is genetically heritable, but the precise “gene for depression” remains obscure. There are at least 44 out of the 20,000 genes in the human genome that contribute to the risk of transmitting depression from one generation to the next.
More surprisingly, many of the risk genes for depression also influence the immune system. There is growing evidence that inflammation, the defensive response of the immune system to threats such as infection, can cause depression. Social stress can also cause increased inflammation of the body. Inflammation could be one of the missing links: stress provokes an inflammatory response by the body, which causes changes in how the brain works, which in turn cause the mental symptoms of depression. But it’s not just illness and infection that causes inflammation. Obesity is also linked with it, especially the fat stored around the middle (61 per cent of adipose tissue consist of macrophages, one of the principal sources of inflammatory cytokines). A combination of habits such as smoking, not exercising and a high-sugar diet increases inflammation.
Despite the prevalence of depressive disorders and the daunting scale of the public health challenge, there are limited ways of dealing with them. There hasn’t been a significant advance in treatment for depression in nearly 40 years.
In Japan, depression is referred to as ‘ kokoro no kaze’, which means ‘a cold of the soul’