As the peak of summer begins, with temperatures reaching 82.4°F (28°C) in the afternoon, many people are avoiding outdoor activities due to the intense sunlight. However, a study has shown that moderate exposure to sunlight can increase the body’s energy expenditure and lead to weight loss.
A research team from the Department of Dermatology at Seoul National University Hospital announced that exposure to ultraviolet rays can prevent weight gain.
The research team fed mice a normal or high-fat diet to understand how ultraviolet rays regulate total body energy metabolism. They were continuously exposed to ultraviolet rays three times a week for 12 weeks. They then compared the groups with control groups of mice that consumed the same diets but were not exposed to ultraviolet rays.
The study found that the expression of leptin (an appetite-suppressing hormone) secreted from subcutaneous fat decreased in mice exposed to ultraviolet rays. As a result, their appetite increased, and they consumed more food than the control group of the same diet. However, despite their increased appetite, the mice exposed to ultraviolet rays lost weight compared to the control group.
“The white fat in the mice exposed to ultraviolet rays turned into brown fat, resulting in greater energy expenditure than food intake,” the research team explained.
Fat is categorized into white fat, which stores energy, and brown fat, which generates heat to burn the energy. Unlike white fat, which stores fat obtained from food as triglyceride, brown fat burns the body fat. Therefore, despite the greater food intake, the increase in brown fat resulted in a more significant fat burn, preventing the accumulation of triglycerides.
The research team explained that this phenomenon occurs because exposure to ultraviolet rays releases norepinephrine, a metabolic hormone that acts on the sympathetic nervous system in dangerous or stressful situations.
The skin of mice exposed to ultraviolet rays contained an increased level of norepinephrine. When this hormone was artificially blocked in these mice, their food intake decreased, but their brown fat decreased, leading to weight gain.
The research team highlighted that exposure to ultraviolet rays boosts the expression of norepinephrine in the skin, affecting appetite, weight, and other metabolic activities. Based on these results, they noted that ultraviolet rays could play a significant role in controlling metabolic diseases, including obesity.
However, they also warned, “Ultraviolet rays are a major cause of skin aging. It’s dangerous to stand under the sun excessively to lose weight. It’s recommended to protect your skin with sunscreen before getting sunlight.”
Meanwhile, according to the international academic journal Scientific Reports in the UK, a research team led by Professor Peter Light of the University of Alberta in Canada published a research paper in 2018 stating that the blue light of the sun reduces the size and prevents accumulation of subcutaneous fat cells in the body.
The research team explained that blue light increases the secretion of leptin, the hormone that suppresses appetite, and adiponectin, which improves insulin resistance, helping with weight loss and preventing diabetes.
Light also warned against using excessive sun exposure for weight loss, noting that more research is necessary to ascertain the appropriate duration and intensity of blue light required to activate the breakdown of subcutaneous fat cells.
