Two numbers to remember for a healthy 2017: 42 and S$3,600

NEW YORK — Two numbers are, to me, particularly emblematic of what science had to tell us about fitness this year.

The first is 42 per cent and represents the extent by which people’s risk for premature death rises if they are out of shape, according to a study published in July. That number almost equals the risk of early death associated with heavy smoking.

The second figure is US$2,500 (S$3,600) and is the amount of money that each of us most likely could save annually on medical costs related to heart disease if we walked for 30 minutes most days, according to a wonderfully pragmatic study released in September.

In other words, exercise science this year taught us that being inactive could potentially cost us years from our lives and many thousands of dollars from our wallets.

There were other lessons in this year’s exercise research, of course. Some of the most compelling involved advances in our understanding of how exercise may change our bodies invisibly but pervasively.

A February study, for instance, involved mice with a high risk of developing melanoma. If those animals ran moderately on wheels, their immune systems changed in ways that enabled them to combat the cancer. They produced more of a type of immune cell known to fight malignancies than did sedentary animals and were much less likely to develop invasive disease.

Exercise, in other research this year, also was shown to prompt muscles to release substances that wind up changing the structure and function of the brain.

For a study I wrote about in July, scientists at the National Institutes of Health isolated a protein created abundantly in muscles during exercise.

They then applied the protein to neurons in Petri dishes and found that the cells started producing other substances that can help generate additional neurons. Working the body’s muscles, in effect, changed brain cells in ways that increase neuron numbers.

Fat cells likewise were transformed by exercise, another study found.

In it, researchers from the University of Florida injected a hormone produced during and after exercise into normal human fat cells.

These cells consisted of white fat, which is metabolically lazy, burning few calories.

But after exposure to the exercise-related hormone, some of the fat cells began to display molecular markers indicating that they were becoming brown. Brown fat is metabolically active; it burns calories.

So exercise, according to this finding, may contribute to metabolic health by producing a hormone that can brown human fat.

Not all of the news about exercise this year was reassuring, of course.

A worrisome study published in August reported that young people who had sustained at least one concussion were much more likely than those who had never had a head injury to underperform in school and, as adults, experience lingering mental and physical problems.

Another cautionary study this year found that stopping exercise, even for just 10 days, changed how much blood flowed to volunteers’ brains.

In that experiment, longtime masters runners underwent brain scans and then abruptly stopped working out for a week and a half. A subsequent scan showed that they were now pumping less blood to their brains, and in particular, to portions of the brain involved in memory and learning.

The slightly discomfiting message is that if we wish to realise all of the benefits of exercise, we probably have to continue exercising throughout our lives.

On the other hand, the benefits of being active do seem to be nearly incalculable, as other 2016 studies underscored. The various studies showed that exercise of almost any amount may substantially lower risks for depression, muscle wasting, at least 13 types of cancer and colds.

But as the near year approaches, I’ll return to the research concerning the decidedly calculable advantages of being active, including the 42 per cent increased risk of dying too young if you are unfit and the US$2,500 in annual savings potentially enjoyed by those who get out and walk.

I have plans for those years and those dollars. I hope you will join me in walking, fidgeting and otherwise moving and working out in 2017. Happy holidays. THE NEW YORK TIMES