It might be time we add exercise to masks, social distancing and good hand hygiene as the best protection against COVID-19.

Exercising about 22 minutes daily could reduce your risk of severe illness or death, according to a new study by researchers and physicians at the Kaiser healthcare system in California who reviewed anonymous records of 48,440 adult patients diagnosed with COVID-19 from January-October 2020. Kaiser had asked all patients to add exercise habits since 2009 as a vital sign, allowing researchers to group men and women by their reported physical activity.

The least active were hospitalized almost twice as much and were 2.5  times more likely to die than the most active people, according the study published this week in the British Journal of Sports Medicine.

The least active group said it exercised 10 minutes or less a week. The most active group, meanwhile, said it achieved the U.S. Department of Health and Human Services’ recommended 150 minutes or more a week of moderate-intensity aerobic activity.

The researchers also considered each patient’s preexisting conditions and other risk factors such as age, weight and a history of smoking. Advanced age and an organ transplant were the only other risk factors stronger than a sedentary lifestyle among patients with severe COVID-19 outcomes.

So how does exercise help people avoid serious illness? A study last year by the National Institutes of Health might have an answer: It associated regular exercise with a heightened immune system response that could help the body reject COVID-19 and other illnesses.

A recent Harvard University study found health benefits in even less regular physical exercise than prescribed by one set of federal guidelines that recommends 10,000 steps a day. The new research found similar benefits, particularly among women, in only 4,400 steps a day. A mile is about 2,000 steps.

“This illustrates the importance of being active,” said Dr. Stephanie Saucier, a cardiologist and director of the Women’s Heart Wellness Program at Hartford HealthCare’s Heart & Vascular Institute. “I recommend all of my patients who are physically able exercise regularly — about 150 minutes of moderate intensity exercise per week with some strength training included. The most benefit for people is when they go from being sedentary to being active.”