A new national survey from the Nature & Health Alliance found that nearly half of Americans spend less than two hours outdoors in an entire week. The survey involved researchers at Texas A&M University.

Dr. John La Puma, a California physician and expert in nature based medicine, has focused on the potential health effects of limited outdoor time. In his book, “Indoor Epidemic,” he says humans spend about 93% of their lives inside.

La Puma describes the consequences as a “hidden health tax” and proposes a simple 7% outdoor prescription. He connects excessive indoor time with problems involving the body clock, burnout, mental fog and altered cortisol activity associated with abdominal and visceral fat.

The physician described people who remain exhausted after a full night of sleep, rely on coffee to feel normal and crash at 2 in the afternoon. Some feel wired at night and struggle to fall asleep even when their laboratory results are normal.

Outdoor light can be many times brighter than typical indoor lighting, according to La Puma. That brightness provides a powerful signal for setting the circadian rhythm, the internal clock that helps determine when the body sleeps and wakes.

Getting bright outdoor light soon after waking can help synchronize that cycle and support the natural rise in melatonin later in the evening, La Puma said. He recommends spending about 10 minutes outdoors without sunglasses during the first hour after waking.

La Puma uses the term “ultraprocessed time” for hours consumed by screens, scrolling and other digital distractions. He compares that time with ultraprocessed food, describing both as lacking nourishment while being synthetic, artificial and widespread.

Endless scrolling can make time seem to evaporate, he said. La Puma argues that a person’s surroundings can contribute to burnout, rather than treating the condition solely as a failure of willpower.

Excessive indoor time can also produce an overload of screen exposure because people frequently use the same devices for work, entertainment and relaxation. La Puma said the body may not interpret time on those devices as genuine rest or escape.

Indoor environments also restrict how far people can see, leaving them deprived of horizon views. “Your eyes need distance like your lungs need air,” La Puma said.

To counter burnout, he recommends standing up once every hour, walking to a window and looking outside for one minute. “It relaxes your eyes, relaxes the muscles around your temples, reduces headache if you have it, improves energy and reduces fatigue,” he said.

Mental fog can become particularly noticeable by the afternoon in poorly ventilated spaces, La Puma said. Indoor carbon dioxide levels can rise above 1,000 parts per million, and some research has linked elevated levels with reduced cognitive performance.

Ventilation can be difficult to improve in an office or conference room, according to the physician. The EPA also notes that concentrations of some pollutants can be two to five times higher indoors than outdoors.

Going outside offers a break from potentially stuffy indoor air while allowing the eyes to focus at greater distances. When leaving is not possible, La Puma recommends looking through an open window or focusing on a distant rooftop rather than remaining visually confined by an indoor space.

An out of sync body clock can disrupt the body’s normal cortisol rhythm, La Puma said. Research has linked altered cortisol activity with greater abdominal and visceral fat, although the relationship is complex.

Cortisol naturally rises and falls throughout the day, and La Puma recommends getting daylight at the right time, particularly early in the morning. He said this produces an early cortisol increase that supports wakefulness before the level drops appropriately.

La Puma distinguishes purposeful outdoor exposure from the incidental time people accumulate while walking between a car and an office. He recommends at least 17 minutes each day in a blue or green space as the minimum effective dose.

That outdoor period should be intentional, he said, with people looking at the morning sky, watching clouds and giving their body clock a clear signal. For city residents without a sky view, focusing on a distant rooftop can still extend vision beyond the confines of a room.