Every time seeing the sunshine outside the window, people usually want to go out for a walk, breathe some fresh air, and improve bone quality! However, do you worry about the risk of cancer caused by sunlight? Regarding this contradiction, we will divide the following discussion into two parts. Let's move on!

---

【Relationship between sun exposure and skin cancer】

There has been sufficient scientific evidence to confirm that solar radiation is one of carcinogens, and it has been identified as a group 1 carcinogen by the International Agency for Research on Cancer (IARC) under the World Health Organization (WHO). (for detailed explanation, please read the previous article 【Let's prevent from cancer earlier】). The cancer related to solar radiation is mainly skin cancer.

However, we should have a deeper understanding of the carcinogenicity of solar radiation, in order to avoid losing the health benefits of sunlight due to excessive avoidance of the sun.

Regarding the dose-response relationship between solar radiation and skin cancer, It's discussed in great detail in the paper 《The relationship between UV exposure and incidence of skin cancer》. Three different types of skin cancer are discussed in this paper: Squamous Cell Carcinoma (SCC), Basal Cell Carcinoma (BCC), Cutaneous Melanoma (CM). The incidence of skin cancer per unit area on the skin is taken as Relative Tumor Density (RTD). And the research team quantified the UV light exposure intensity by the number of joules received per square meter. Finally, they used regression models to analyze the relationship between the UV light exposure intensity and the incidence of skin cancer.

It can be seen from the chart in the paper that the relationship between UV light exposure intensity and the incidence of the three types of skin cancer is very close to a linear positive correlation or an exponential linear positive correlation, which means that there is a clear dose effect between the two:The more UV light exposure, the incidence of skin cancer will increase. The detailed dose-response relationship is about: UV light exposure intensity increased by 2 times, and the incidence of three types of skin cancer increased by 2 to 4 times.

BUT!!! If you dig deeper, you will know thatThe carcinogenicity of solar radiation to skin cancer of different races is different! In WHO official website, it shows that race-related risk factors for skin cancer include: (1) fair skin (2) blue, green, or hazel eyes (3) light-colored hair, which can be proved by the data provided by theU.S. Centers for Disease Control and Prevention. As shown from the figure below, the skin cancer incidence of Asians is much lower than that of whites:

However, although solar radiation is less carcinogenic to Asian skin cancers, we must also pay attention to other risk factors mentioned in the WHO official website , such as:Skin that is more susceptible to sunburn, has had a major sunburn in the past, has many moles or freckles, has a family history of skin cancer. If you have these risk factors, then the carcinogenicity of solar radiation to you will be relatively higher.

---

【The effect of sun exposure on bones】

With regard to the research 《Determinants of bone health in adults Polish women: The influence of physical activity, nutrition, sun exposure and biological factors》, It is commendable that the research team quantified the physical activity intensity, nutritional status, and sunlight exposure intensity of the subjects in detail. Also, they measured the bone density at the proximal and distal ends of the forearm. Finally they incorporated the above data into the model analysis, and then got more clearer understandings of the relationships between bone density and these above-mentioned factors.

The results showed thathaving normal bone density is significantly related to the following factors:
("OR" stands for odds ratio. You can find more information about "OR" in bio-statistics books)

(1) ForDistal forearm:
– Sufficient calcium intake (OR = 5.95)
– "Past" medium-intensity (OR = 1.88) or high-intensity (OR = 14.0) physical activities
– "Present" medium-intensity (OR = 4.97) or high-intensity (OR = 18.9) physical activities
– Sufficient sunlight in the “past” (OR = 5.15)
- Sufficient sunlight "now" (OR = 10.0)

(2) ForProximal forearm:
– Sufficient calcium intake (OR = 9.57) and vitamin D intake (OR = 2.68)
– "Past" medium-intensity (OR = 4.20) or high-intensity (OR = 68.4) physical activities
– "Present" medium-intensity (OR = 6.13) or high-intensity (OR = 10.0) physical activities
– Sufficient sunlight in the “past” (OR = 10.6)
– Sufficient sunlight "now" (OR = 9.09).

From the above results, it can be found that regardless of the bone density of the proximal or distal forearm,physical activity intensity, sunlight, calcium intakeare all important factors. Among them, the odds ratio of "high-intensity physical activities" is higher. Therefore, in order to have normal bone density, you shouldmaintain the habit of high-intensity outdoor activities and get enough calcium in your diet.

---

Based on the above, for Asians, the carcinogenicity of solar radiation in skin cancer is relatively low. If considering the benefits of sunlight on bone density, we believe that people should not constantly stay indoors to avoid the sun exposure. Especially in modern urban life, people generally lack the intensity of physical activity due to the popularity of office work. Therefore, we encourage everyone toengage in outdoor activities or sports more often, but avoid excessive sun exposure that can cause sunburn. Besides, getting enough calcium and vitamin D intake from food is also very important. (Most people have insufficient calcium and Vitamin D intake).

Finally, we wish everyone can have good bone health!

〈The author is former Attending Physician in National Taiwan University Hospital, and Master of Science from National Taiwan University〉