Anyone who still needs convincing that increasing their physical activity is worthwhile may gain motivation from research showing that, in addition to reducing the risk of certain forms of cancer, it might also slow the rate at which the disease progresses.
In a study presented at the Physiological Society’s annual conference this month, Dr Sam Orange, a lecturer in exercise physiology at Newcastle University’s Centre for Cancer, found that a single exercise session releases substances into the bloodstream that can have an immediate impact on slowing down the growth of cancer cells.
The idea that exercise, in addition to its many other health benefits, helps to reduce our susceptibility to cancer is already compelling.
A slew of emerging evidence suggests other things are at play when it comes to the risk-reducing role of exercise
According to Cancer Research UK, “the more active you are, the better”, and in a paper entitled Exercise Is Medicine in Oncology, a distinguished panel of researchers from the American College of Sports Medicine calculated that regular exercise can lower the risk of getting some cancers by as much as 69 per cent. Others have shown how sitting for hours at a time can raise your risk of dying from cancer significantly compared with those who sit the least. Some of the benefits of activity are undoubtedly down to the resulting weight loss – obesity is a risk factor for many types of cancer, so a positive move on the scales as more calories are gobbled up is welcomed.
What intrigues researchers such as Orange, though, is a slew of emerging evidence that suggests other things are at play when it comes to the risk-reducing role of exercise. In one large-scale epidemiological study published in the journal JAMA, scientists from the US National Cancer Institute, Harvard Medical School and other research bodies found that active people were much less likely to develop 13 types of cancer than their sedentary counterparts. Those results held true regardless of their weight. In other words, overweight or obese people who moved a lot were at a lower risk of these cancers than those with a similar BMI (body mass index) who spent too much time sitting down. “Studies show that, even after accounting for body fatness, exercise is helpful in reducing the risk of cancer,” Orange says.
“The question we want answering is, if it’s not weight loss, what are the mechanisms that explain the link between regular physical activity and reduced cancer risk and slowed tumour growth.”
For this preliminary study, the results of which are soon to be submitted to a peer-reviewed journal, his team recruited 16 middle-aged men, all of whom had lifestyle risk factors for bowel cancer, including that they were overweight, 50-plus, and largely sedentary. After providing initial blood samples, the participants cycled on indoor bikes at a steady pace for six five-minute bouts, each separated by a few minutes of gentle active recovery. This was not high-intensity interval training (HIIT), he says, but a much more gentle form of intermittent training – enough to leave them puffing but not exhausted. After they had finished pedalling, they then provided a second blood sample, and the researchers also took before-and-after blood samples during a non-exercise control experiment. Blood samples were then compared.
Orange wanted to find out whether exercise altered the concentration of specific cancer-fighting molecules in the blood. “We know from previous research that changes in circulating blood levels of some hormones, such as adrenaline and glucagon, and small proteins might affect the growth of cancer cells,” he says. “And we saw a rise in levels of a particular type of protein called interleukin-6 [IL-6] released by muscles after a single half-hour of moderate exercise.”
It is thought that exercise can also increase the activity of immune cells in the blood, which can further help to inhibit cancer growth.
The role IL-6 plays in cancer depends on the tissue from which it is released. In some circumstances it has a pro-inflammatory action and promotes tumour growth, but when released from muscle during exercise it can bind directly to cancer cells, preventing them from getting bigger. To demonstrate this, Orange added the blood serum samples to bowel cancer cells in the lab and monitored cell growth over 48 hours. Compared with non-exercise samples it slowed significantly.
There were some limitations to the study. “The cancer cells were grown in a dish under tightly controlled conditions,” Orange says. “In real life human cancer tumours are complex and interact with the environment, including blood vessels and immune cells, that surround them.”
It is thought that exercise can also increase the activity of immune cells in the blood, which can further help to inhibit cancer growth. At the Karolinska Institute in Sweden molecular biologists showed how exercise changed the metabolism of cytotoxic cells of the immune system, improving their ability to attack cancer cells. Orange says all of the new findings provide a huge step forward in understanding the role exercise can play in cancer prevention. For his next study he will look more closely at how exercise for people with cancer could slow disease progression. “We will be investigating whether there is a cumulative effect and how the type of exercise could potentially impact cancer cell growth,” he says.
He has already shown that the more often you move – in any way you can – the better. After trawling the literature for studies linking physical activity with slowed cancer cell growth last year, Orange and his colleagues discovered that repetitive spikes in beneficial circulating hormones and proteins after frequent bouts of exercise may accumulate over time to progressively reduce cancer risk and tumour growth.
Binge workouts every weekend are not the best approach. “When exercise is repeated multiple times each week over an extended period, it’s possible that these exercise-induced factors in the bloodstream have multiple opportunities to interact with cells throughout the body, potentially resulting in a more pronounced suppression of cell growth,” he says. “Being physically active on several days per week, rather than accumulating all weekly activity across one or two days per week, may be particularly important for reducing cancer risk.”
It also seems that you do not need to push yourself to sweaty extremes in every workout to bring benefits. Brisk walking, jogging, and cycling all tick the box, as do regular yoga, t’ai chi and pilates. “In our meta-analysis we looked at whether the intensity of exercise affected the growth of cancer cells. But there was no evidence that vigorous exercise was any more beneficial than moderate activity.”
At 28, Orange cycles three times a week and lifts weights three times weekly, a habit he intends to continue. But every little helps he says. If you do sit at your desk all day, regularly getting up for a few minutes to walk around the office might lower the risk of dying from cancer, found oncologists at the University of Texas. In that study of 8,002 middle-aged, activity-tracker-wearing volunteers, who spent an average of 13 hours a day in the parked position, even raising themselves out of the chair for ten minutes at a time resulted in their risk of dying from cancer being reduced by 8 per cent. If they replaced some sitting with half an hour of light intensity activity, they were 31 per cent less likely to die from the disease.
Orange says there is mounting evidence to support exercise becoming a supplementary therapy to cancer treatments, as well as an important step towards cancer prevention. “There’s a push to get exercise added as part of the package in standard cancer treatment pathways. Physical activity is cheap and inclusive, plus it brings back a sense of control for cancer patients as it is something they can take on themselves if they wish. It has few side effects, many benefits and could make a real difference to people’s lives.”
