It’s the most basic common sense: Exercise is essential.

But not at Mars High School, where the board is considering a proposal to cut the physical education requirement from one course per year to one every other year.

At the Mars school board meeting Tuesday night, high school Principal Todd Kolson recommended that the physical education requirement be reduced so that students must take PE once during their freshman or sophomore year, and again during their junior or senior year.

The current requirement — indeed, the long-running standard for any public high school — is one semester of PE per year.

The students still would be able to take PE every year during high school if they so choose, Kolson said, and students carrying a heavy academic load still can earn PE credits through independent study.

But for the majority of Mars students, gym might become an every-other-year requirement.

Apparently it’s a financial decision. Kolson said requiring two instead of four PE classes during the high school years would preclude the district from having to hire another PE teacher.

But that’s a short-sighted and even illogical proposition.

Consider the growing epidemics of obesity and diabetes.

Nearly 78 million adults and 13 million children in the United States are struggling with the physical and emotional effects of obesity, while 18 million are diagnosed with diabetes — that compares with 5.8 million diagnosed diabetics in 1980.

The trends are accelerating: It’s estimated that one in three Americans living today eventually will develop diabetes.

The cost of treating diabetes is astronomical. A study commissioned by the American Diabetes Association in 2013 concluded the annual cost of treating diabetes in 2012 was $245 billion, including $176 billion in direct medical costs and $69 billion in lost productivity. That comes out to an average of more than $13,000 a year for every diabetes patient. Medical policy directors warn us that diabetes is on track to eventually “break the bank” of health care coverage.

And the best way to prevent diabetes is diet and exercise.

Our first lady has the diet part covered. Michelle Obama’s initiative, the Healthy, Hunger-Free Kids Act, limits the calorie intake in school lunches to 750-850 calories.

But for the exercise component, it’s generally accepted that we all could use some help.

There is increasing recognition that physicians simply instructing patients to eat better and get more exercise isn’t working. The American Council on Exercise, a nonprofit advocacy group, states that “patients lack the support and ability to turn that basic guidance into meaningful, long-term behavior change,” and “the U.S. population lacks literacy in the quantity and types of physical activity recommended in the U.S. National Physical Activity Guidelines.”

In other words, young people trying to establish healthy lifelong habits need a trained expert to help them. This is particularly true for less-motivated young people — the kind who, if given the choice, would opt out of a physical education class.

In today’s education system, is there any lesson more important than the one that strives to establish a lifetime of health and productivity? Reduction of the PE requirement minimizes the importance of this lesson; it fails to establish and sustain healthy habits; it will rob some individuals of small fortunes in future medical treatment, lost productivity and quality of life.

All to save the expense of hiring another PE teacher.