42 | APRIL 2016
Professor Tim Olds leads the Health and Use of Time Group at the Sansom Institute for
Health Research, University of South Australia.Choose Your Friends Wisely
Friends, family and co-workers influence our
health and happiness to varying extents.When asked about what one could do to improve one’s itness,
the renowned exercise physiologist Per-Olof Åstrand replied:
“Choose your parents wisely”. Now it seems that to improve our
health we have to do more than choose our parents: we need to
choose our friends because disease (and health) can spread through
our real and virtual social networks.
One US study that followed 12,000 people for 32 years found
that your risk of becoming obese increases by about 40% if you have
a sibling or spouse who becomes obese (tinyurl.com/zptcb86).
The important factor is social distance (e.g. being the friend of a
friend) rather than geographical distance. You won’t become
obese if the people next door you never speak to become obese,
but if your best friend on the other side of town fattens up, you’re
more likely to put on the kilos as well.
The love also has to be mutual. Your risk of obesity is unaf-
fected if your soon-to-be-obese acquaintance considers you a
friend but you don’t. If you consider them a friend, but they don’t
consider you a friend, your risk goes up by 57%. If you both
consider each other friends and your friend becomes obese, your
chances of becoming obese nearly treble (171% increased risk). It
may be time to ind that “unfriend” button on Facebook.
Even death can travel through social networks. A very early
study found that your risk of attempting suicide is four times
higher if you have a friend who has already done so
(tinyurl.com/hm2rfk6).
While death and obesity are among the near certainties of life,
it stands to reason that if bad things can spread among friends, so
can good things. Happiness spreads through social networks like
head lice through a kindy class (tinyurl.com/hlp7byr). Your
chances of becoming happier increase if you rub shoulders with
people who become happy. If your next-door neighbours become
happy, your chances of becoming happy increase by 34%. If a
friend living within 1.6 km becomes happy, your chances of
becoming happy increase by 25%. The happy rays emitted by
siblings (14%) and spouses (8%) are apparently less strong, Newly
happy co-workers have no effect at all, so it’s OK to be grumpy at
work.
Quitting smoking can also spread from friend to friend
(tinyurl.com/jxsa6jr). If your signiicant other quits, you have a
67% decreased chance of smoking.
Health and disease may run through online networks as well
as face-to-face networks. A recent review of the use of online social
networks as a vehicle for health interventions by my colleague Dr
Carol Maher showed promising results (tinyurl.com/jnd2v9c).
More skeptical readers of Australasian Sciencewill doubtless be
asking themselves at this point whether all this couldn’t be due tocclike people attracting like. While it’s true that obese people are
more likely to befriend other obese people, this doesn’t explain the
increased probability of becoming obese.
Of course, it’s possible that people in the same social network
share characteristics that incline them to obesity (they may be
part of the same baking circle, or enjoy sedentary leisure pursuits
like video games). Only a randomised controlled trial would settle
this question. We could surreptitiously insert people into social
networks – say smokers and non-smokers – and see what the
network effects are but I can’t see this going down well with ethics
committees.
Some researchers have even exploited social networks to spread
health interventions. In Honduras, researchers wanted to intro-
duce a multivitamin supplementation program
(tinyurl.com/z7avqmr). The idea was to spread the program via
word of mouth, starting with 5% of villagers. In some villages,
researchers randomly selected the initial targets, and in other
villages they randomly selected individuals, asked them to name
a friend, and then these nominated friends became the initial
targets.
While it wouldn’t seem to matter whether you chose a random
person or their friend. But it did. Uptake of the multivitamins
was signiicantly higher in the villages where the initial targets
were the nominated friends. This interesting oddity arises from
the “friendship paradox”: on average your friends will have more
friends than you have (tinyurl.com/z59p8rh). More worryingly,
it means that your sexual partner will probably have had more
sexual partners than you have had. The friendship paradox arises
from a sampling bias, whereby people with a greater number of
friends are more likely to number among your friends. Ditto
sexual partners: if people sleep around a lot, they’re more likely to
be sleeping around with you.
Remember that. There’s nothing wrong with sleeping around
— but just make sure they’re not getting fat.Ariwasabi/AdobeTHE FIT Tim Olds