Summary
Highlights
A 2011 Swedish study followed 20,000-30,000 women for 20 years, categorizing them by sun exposure (low, moderate, high). The astonishing finding was that women with the most sun exposure had the lowest mortality from cancer, cardiovascular disease, and non-cardiovascular diseases. Conversely, those with the least sun exposure had the highest mortality rates. The study even suggested that low sun exposure posed a similar mortality risk as smoking, as sun-exposed smokers had the same mortality as non-sun-exposed non-smokers.
While the Swedish study was an association study, the concept of a 'dose-response curve' can strongly suggest causation, similar to how smoking was linked to lung cancer. Richard Weller's UK Biobank study, 10 times larger and including both men and women, replicated these findings. It showed that more light exposure (from sun or solariums) correlated with lower mortality risk from non-skin cancers. Crucially, it found no statistically increased risk of melanoma incidence but a reduction in non-skin cancer mortality. This led to a re-evaluation of public health advice regarding sun exposure.
The speaker argues that a mere 15 minutes of daily sun can improve mitochondrial function, impacting overall health. Modern society spends increasingly less time outdoors, 93% for Americans and 92% for Brits. This lack of sunlight is likened to the 'scurvy of the 21st century.' Our ancestors spent significant time outside, engaging in physical activity and breathing fresh air. Even modern windows are designed to block infrared light, a beneficial component of sunlight that can penetrate clothing and skin to interact with deep heat receptors.
Infrared light is highly reflected by trees, meaning green environments offer more beneficial infrared exposure than concrete jungles. Studies have long shown that people in green spaces have better health outcomes for diabetes, hypertension, and depression. The 'GreenHeart study' in South Louisville, Kentucky, demonstrated a direct impact. After planting 8,000 mature trees in a 4-square-mile area, participants' inflammation markers (HS-CRP) dropped by 13-20% within two years, correlating to a 10-15% reduction in strokes, without changes in socioeconomic status or exercise habits. This suggests a direct health benefit from green environments independent of other factors.
Modern LED and fluorescent bulbs, designed for efficiency, emit a narrow spectrum of light primarily focused on blue light, lacking the broad spectrum of traditional incandescent bulbs or natural light sources like fire and sunlight. This is a novel exposure for humanity. A preprint study by Glenn Jeffrey showed that switching from LED to incandescent bulbs improved color differentiation by 25%. This is because the retina, rich in mitochondria, relies on broad-spectrum light for optimal function. Short, targeted exposure to 670 nanometer red light (similar to red light masks) has also been shown to improve vision in older individuals by boosting mitochondrial energy output in the eyes.
Mortality rates for various diseases, including cardiac, respiratory, and infectious diseases, consistently peak about a month after the shortest day of the year (December/January in the Northern Hemisphere). This pattern holds true globally; Australia, in the Southern Hemisphere, sees its highest mortality during its winter months (June/July), despite holiday gatherings. This strong correlation suggests that the length of the day, a proxy for sunlight exposure, significantly impacts overall health and mortality. Many individuals, especially those in shift work, can go weeks without seeing the sun during winter months.
For those concerned about UV damage, the optimal times for sun exposure are in the mornings and evenings when the sun is low in the sky. During these times, the atmosphere filters more UV light, allowing a higher proportion of beneficial infrared light to reach us. At noon, when the sun is directly overhead, both infrared and ultraviolet radiation are at their highest. Individuals not accustomed to much sun exposure may want to avoid this period or use protective clothing while still benefiting from the infrared light, which penetrates well through clothes.