7/25/2019 Cancer - A Run a Day Keeps the Tumor at Bay

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Cancer 

 A run a day keeps the tumour at bay 

Exercise protects against cancer. Researchers now understand why

 AMPLE evidence shows that exercising regularly reduces the risk of cancer. Similarly, those who

have survived the disease are less likely to see it return if they engage in lots of physical activity

after treatment. All this suggests that such activity triggers a reaction in the ody which somehow

thwarts cancer cells, ut the details of the process have remained murky. !ow, a team led y

Pernille "o#man at $openhagen %niversity "ospital, in &enmark, has reported in Cell

Metabolism that the key to the mystery is adrenalin.

&r "o#man egan her work y verifying that exercise truly does have eneficial anti'tumour effects.

She and her colleagues gave some of the mice in their laoratory activity wheels, which the animals

could run around inside as much as they liked. (ther mice, meanwhile, were given no opportunity to

exercise eyond moving aout inside their cages. )he researchers then induced mice of oth sorts

to develop one of three types of cancer. Some, they in#ected with a sustance called

diethylnitrosamine, which causes liver cancer. (thers, they in#ected elow the skin with melanoma

cells, which then set up shop where they had een in#ected. (thers still had their tails inoculated with

melanoma cells. *n mice, previous experience has shown, this leads to melanomas forming in the

lungs.

In this section

• )aking a ite at the Apple• A run a day keeps the tumour at bay

• !ow is the time to say +goodye

• Plucking ruies from the ruish

• -idelio

• $ancer 

• "ealth and fitness

)he results were instructive. hile all mice in#ected under the skin with melanoma cells developed

that cancer, the tumours in animals which had had access to a running wheel were /01 smaller

after six weeks than were those in mice that had een unale to exercise. A similar reduction in si2e34516 pertained to lung tumours. And, of the mice in#ected with diethylnitrosamine, only 701 of

those with wheels in their enclosures developed tumours at all8in contrast to a 941 tumour'

development rate in mice lacking access to a wheel.

)o try to understand why exercise does this, &r "o#man and her team put under a microscope some

of the tumours they had induced. )hey found that those from well'exercised mice contained more

7/25/2019 Cancer - A Run a Day Keeps the Tumor at Bay

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immune cells than e:uivalent tumours from inactive animals. Specifically, the former had doule the

numer of cytotoxic )'cells, which kill off ody cells that are damaged, malfunctioning or infected

with viruses. )hey also had five times more natural killer cells, a type that sounds the alarm and

attracts other immune cells.

*n light of these discoveries &r "o#man repeated the experiment, this time on mice that had een

engineered to lack cytotoxic )'cells. Again, she found that mice with access to wheels had smaller

tumours. )his suggested that the natural killer cells, not the )'cells, were the responsile agents. A

third experiment confirmed this. She saotaged natural killer cells y giving mice an antiody that

eliminated these cells while leaving the rest of the immune system intact. ith the natural killer cells

gone, the tumours of all the mice, regardless of whether or not they could run in a wheel, grew to the

same si2e.

&r "o#man knew from past work that epinephrine, a hormone also commonly known as adrenalin,

has the potential to moilise natural killer cells. She knew, too, that this hormone;s levels in the loodrise during periods of physical exertion. )hat led her to wonder if it is epinephrine which is ehind the

cancer'thwarting effects of exercise.

)o find out, she ran a fourth experiment, in which mice induced to have cancer were in#ected either

with epinephrine or with saline. )he hormone performed well, reducing the growth of tumours y

/01 in mice that had no access to a wheel. "owever, this was not as impressive as the reduction of

9<1 which the team saw in control mice that got regular exercise. )here was, they concluded,

something else involved. And they found it in the form of interleukin'/.

Levels of this molecule also spike during exercise8and it, too, helps immune cells home in ontumours. hen &r "o#man and her colleagues exposed sedentary mice oth to epinephrine and to

interleukin'/, the rodents; immune systems attacked the tumours in their odies as effectively as if

those animals had engaged in regular wheel'runs.

&r "o#man;s findings, then, suggest that epinephrine and interleukin'/ could e used as anti'tumour

drugs. She is not proposing that they should e a sustitute for exercise in those who are merely

la2y8not least ecause exercise rings enefits eyond curing oncogenesis. =ut people who are

too old or too ill to e active might thus gain exercise;s anticancer enefits without the need to get

sweaty.

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