What studies demonstrate ultraviolet (UV) radiation from sunlight causing cancer, as opposed to artificial light?

From the Guidelines

Exposure to natural sunlight, specifically its ultraviolet (UV) radiation, is a proven cause of skin cancer, and individuals should take protective measures to minimize their risk. The evidence from the US Preventive Services Task Force recommendation statement 1 highlights the importance of reducing UV radiation exposure to prevent skin cancer. Key findings from this study include:

• The incidence of melanoma has been increasing among white Americans, with approximately 70,000 cases and nearly 8,800 deaths in 2011.
• Epidemiologic evidence links ultraviolet radiation exposure with incidence of all three types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma.
• The USPSTF found convincing evidence linking UV radiation exposure during childhood and youth to a moderately increased risk for skin cancer later in life. To minimize the risk of skin cancer, individuals can take the following protective measures:
• Use broad-spectrum sunscreen with a sun-protection factor of 15 or greater
• Wear hats or other shade-protective clothing
• Avoid the outdoors during midday hours (10 a.m. to 3 p.m.)
• Avoid indoor tanning It is essential to recognize that individuals with fair skin, light hair and eye color, or freckles or who sunburn easily are at increased risk for skin cancer 1. By taking these protective measures, individuals can reduce their risk of skin cancer and minimize the harmful effects of UV radiation exposure.

From the Research

Studies on Sunlight and Cancer

• The study published in 2018 2 found that exposure to ultraviolet (UV) radiation from sunlight is the main risk factor for skin cancer, and a major source of vitamin D.
• Another study from 2021 3 noted that UV exposure, whether from natural or artificial sources, is not the ideal way to synthesize vitamin D, and that there is conflicting evidence regarding the relationship between vitamin D, non-melanoma skin cancer, and cutaneous melanoma.
• A 2014 study 4 suggested that the optimal time for sun exposure to minimize the risk of skin cancer while maximizing vitamin D synthesis is between 10 a.m. and 1 p.m.
• The 2022 study 5 highlighted the carcinogenic effects of sun exposure, particularly for fair-skinned individuals, but also noted that low sun exposure habits can increase the risk of cardiovascular disease and other health problems.
• A 2013 review 6 discussed the controversy surrounding the appropriate amount of sunlight exposure to balance the positive and negative effects of solar UV exposure, noting that while UV exposure causes DNA damage and increases the risk of skin cancer, it also has positive effects on human health through the production of vitamin D.

Key Findings

• Sunlight exposure is a major risk factor for skin cancer, particularly for fair-skinned individuals 2, 5, 6.
• Vitamin D production is an important benefit of sunlight exposure, but it can also be obtained through dietary sources 3.
• The optimal time for sun exposure to minimize skin cancer risk while maximizing vitamin D synthesis is between 10 a.m. and 1 p.m. 4.
• Low sun exposure habits can increase the risk of cardiovascular disease and other health problems 5.