When summer comes, sunbathers flock to beaches, parks and poolsides to bask in the sun's ray. Sunbathing has a long history of being associated with health; ancient Greek athletes sunbathed because they believed it would make them stronger. But does sunbathing actually help burn calories? The answer lies in the relationship between metabolism and heat.
Humans, like all mammals, are endothermic or warm-blooded, meaning that they regulate their own body temperature through internal mechanisms. When the body senses that it is in an environment that is too hot or too cold, it initiates measures to regulate its own temperature, such as shivering in cold environments or sweating in warm ones. Other physical responses to warm temperatures include relaxing the muscles, lowering production of adrenaline, and lowering the rate at which metabolism occurs.
Metabolism is the process by which the body turns food into energy and supplies that energy to cells. This energy can either be from a meal or from reserves stored in the body as fat. The level of energy consumed depends on the body's level of physical activity. A body at rest still consumes a minimum level of energy to maintain basic bodily functions; this is known as the basal metabolic rate or BMR. However, even this minimum level is reduced when the body is very warm.
Sunbathing and BMR
When the body is warm and at rest, the BMR drops to a low level, meaning that the body is consuming fewer calories to keep itself functioning. Since sunbathing involves lying motionless in the sun, it consumes very few calories. Sunbathing can only be said to burn calories in the general sense that doing anything at all burns at least some calories. The body uses up calories, although at a low rate, even while asleep.
Sunbathing and Health
It is not clear how the common misconception that sunbathing is useful for weight loss came to exist. It may be that the idea stems from the fact that sunbathers sweat, giving the impression that they are getting some form of exercise. There are some health benefits to sunbathing: brief exposure to sunlight increases the production of Vitamin D in the body. However, prolonged exposure has many health risks, including increasing the likelihood of skin cancer.