NZ Life & Leisure - - Get Online - WORDS ROSEMARI E WHITE

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’

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