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What is the Connection Between Sunlight and Cancer?

Published by Connealy, MD on June 6, 2024

What is the Connection Between Sunlight and Cancer?

Both excessive sun exposure and insufficient sun exposure pose risks for cancer. Inadequate sunlight can lead to vitamin D deficiencies, significantly increasing the risk of internal cancers such as breast, pancreatic, gastric, and colorectal cancers. Conversely, extreme sunburns are stressful and should be avoided. Striking a balance is crucial for our health. Healthy sun exposure (without burns) is associated with a:

  • 75% reduction in colon cancer
  • 50% reduction in breast cancer
  • 20-40% reduction in non Hodgkin’s lymphoma
  • 50% reduction in prostate cancer
  • 30% reduction in bladder cancer

Research: Sun Exposure Is Associated with Reduced Breast Cancer Risk among Women Living in the Caribbean: The Atabey Study in Puerto RicoWe found lower risk of breast cancer associated with greater sun exposure in a population living with high, continuous sun exposure. This beneficial finding should be placed in the context of other effects of sun exposure.” (PMID: 34810207)

Vitamin D and Cancer:

Countless studies have shown vitamin D levels to have an inverse relation with cancer risk mortality. The body needs sun exposure to produce adequate amounts of bioavailable vitamin D. Healthy levels significantly reduce the risk of internal cancers. This may be due to vitamin D’s role in modulating cell proliferation and immune system function, among others.

Skin Cancer and Sunlight:

There are a few types of skin cancer. The most common one, basal cell carcinoma (BCC), is linked to sun burns. Around 75% of non-melanoma skin cancers are BCCs and this cancer is a readily treatable disease. It has a mortality rate of less than 0.05% and  a 100% survivability rate after 5 years.

Non melanoma skin cancer is different from melanoma. Although melanoma is often referred to as skin cancer because it can start as moles, it grows deeper into the skin and can spread throughout the body. The most worrying type of skin cancer is malignant melanoma. The five-year survival rate for metastatic melanoma is only around 15-20%. This makes melanoma a cancer to be avoided, even though it’s not very common. However, the relationship between melanoma and the sun is complex.

Some Things to Consider About Melanoma:

  • “Paradoxically, outdoor workers have a decreased risk of melanoma compared with indoor workers, suggesting that chronic sun exposure can have a protective effect.” (PMID: 15005091)
  • Melanoma is likely to develop in areas of the body that are not commonly exposed to the sun (between toes, scalp, genitals, etc.) and can grow in places with no sun exposure at all.
  • Despite widespread sunscreen use, rates of melanoma and other skin cancers continue to rise.
  • Melanoma is linked to high estrogen levels.
  • “The public health messages of the past 50 years to avoid sun exposure and to use chemical sunscreens may have contributed to the rise in melanoma incidence.” (PMID: 27942349)
  • Melanoma and other skin cancers are more common in areas with low sun exposure.

Despite expectations, regions closer to the equator with the highest sun exposure do not have the highest rates of skin cancer.

So, if not only sun exposure, what else is causing skin cancer? 

We know that there are several other potential factors: 

  • Hormones: Research shows a direct correlation between excess estrogen and melanoma. Elevated levels can create a microenvironment that allows melanoma to develop, proliferate, and metastasize. Melanoma cells typically express estrogen receptors. One study found a 53% increase in melanoma risk in women on HRT taking estradiol without progesterone. (PMID: 35028367)
  • Chemical exposure: Exposure to certain chemicals, such as those in pesticides, industrial pollutants, or even skincare products, can increase the risk of skin cancer. Benzenes and petroleum products are frequently linked to skin cancer and, incidentally, often used in sunscreens, creams, and lotions. (PMID: 28692192)
  • Diet: Like all cancers diet plays a large role in skin cancer. A diet deficient in nutrients including vitamin A, C, D, and E, and minerals like zinc and selenium, can increase the risk, especially because they are important for mitigating cell damage. (PMID: 25995818)
  • Polyunsaturated fats (PUFAs): Ingesting or topically applying these fats can damage cells. They are highly prone to oxidation, especially when exposed to heat. This can induce DNA damage and increase the potential for cancer. One study found “a direct relation between melanoma risk and dietary intake of fatty acids, particularly PUFAs.” (PMID: 23431289)
  • Inconsistent sun exposure: This is also another major risk factor. Getting large doses at one time without consistently exposing the skin can increase the likelihood of burns and cell damage.

This topic is complicated because each person has their own biological makeup and risk factors for skin cancer. While it’s extremely important to avoid burns, the internal cancers that are associated with inadequate low sunlight exposure and vitamin D deficiency are more aggressive and have worse outcomes. For example, colon cancer has a 5-year survivability rate of 65%, while basal cell carcinomas have a s 5-year survivability of 100%.

The aim here is to clarify that simply going outdoors and spending time in the sun doesn’t automatically mean someone will get melanoma. It’s important to consider that these issues aren’t black and white, and there are countless factors that contribute to an individual’s risk of skin cancer. 

Furthermore, excessive sun avoidance is carcinogenic. In our efforts to avoid the sun (more so than any generation before us), rates of cancer continue to rise. We are designed to receive the sun’s inputs. Achieving a balance between safe sun exposure and protection from harmful UV rays is key to maintaining health and connection to nature. It’s important to make peace with our environment and find a healthy relationship with the sun.

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