Newsletter #237

Howdy friends! This week, I wanted to share two new studies that illustrate the impact of intensity on the effects of physical activity on our two biggest killers: cancer and cardiovascular disease.

I was particularly struck by this Israeli paper examining how hard exercise makes it more difficult for cancer to spread by reprogramming tissues throughout the body to ramp up carbohydrate utilization, creating what the researchers call a “metabolic shield” against cancer. I’ve discussed previously how epidemiological data shows that elite athletes are at substantially lower risk of dying from cancer, but we are only just now starting to understand why strenuous activity seems to have this effect.

There was also a great analysis of data from UK Biobank participants, showing that physical activity in general is beneficial for heart health (duh), but there was substantially greater reduction in risk if more of your total physical activity was intense, even if the total energy expenditure was the same (generally meaning that you’re doing a more vigorous activity for a shorter period). This is particularly encouraging because one of the biggest barriers for most of us is time, and this suggests that you can achieve greater health benefits in a much shorter duration, as long as you’re able and willing to work a little harder.

To learn more, scroll on down 👀

Numerous studies have shown that exercise protects against cancer; however, the reasons for this association are not yet well understood. Researchers affiliated with Tel Aviv University analyzed data from a random sample of 2734 individuals from the Israeli general population who were free of cancer at baseline and were followed for 20 years. Overall, exercise was associated with a lower likelihood of developing cancer, but when the researchers zeroed in on cancer staging, the association became much stronger. Specifically, over the course of the study, subjects who reported regular participation in high-intensity exercise had a 73% reduced risk of metastatic cancer, compared to inactive participants. To gain some insight into underlying molecular mechanisms, the researchers put a group of mice on an exercise program and injected melanoma cells into some of them. Sure enough, the animals that exercised had fewer metastases. How come? When the researchers examined the internal organs of the exercising rodents, focusing upon the places where metastases typically are found, like the lungs and lymph nodes, they noticed that the cells of these organs had enhanced capacity for glucose uptake. It is already well established that intense exercise increases the rate of glucose consumption by skeletal muscle. The researchers suggest that perhaps the stress of exercise, over time, reprograms the tissue of these organs to also take up more glucose in order to compete with the sugar demands of muscle. This, in effect, cuts the supply lines to cancer cells, leaving them without enough fuel to grow in the regions of the body where they’re most apt to proliferate. Importantly, it really needs to be intense exercise, like at or above 80% of your max heart rate, to trigger these adaptations.

Broadly speaking, when it comes to physical activity and heart health, more is usually better. But it isn’t totally clear to what extent intensity of exercise matters, in part because activity intensity is often not measured objectively in observational studies. To assess this more rigorously, researchers in the UK looked at data from 88,412 middle-aged adults who did not have cardiovascular disease at the start of the study, and who were followed for almost 7 years. The subjects wore activity trackers on their wrists for a week, from which the researchers were able to estimate total physical activity expenditure as well as amounts of exercise at various intensities. Much as you would expect, total physical activity volume was strongly associated with lower risk of going to develop heart disease in this population. However, there was a further reduction in cardiovascular risk when more of that volume came from moderate-to-vigorous exercise — even when achieving an equivalent energy expenditure. So, this would mean that lightly jogging for 7 minutes would theoretically be better than walking for 14 minutes, despite burning the same number of calories. That having been said, the lowest cardiovascular disease rates were seen in those with higher overall amounts and a greater proportion of moderate-to-vigorous activity — so every little bit of movement counts.

To learn more about how it works, and how it could enhance your own training, check out our past interview with Brad Dieter (Blog)

https://mailchi.mp/humanos.me/newsletter-237