Sunlight and Vitamin D

Introduction
Nutrients are undoubtedly the essential facets that add vigor and vitality to the human body. Vitamin D, affectionately called the sunshine vitamin, plays a crucial role in regulating various body processes. Since it’s a fat-soluble vitamin, its requirement to sustain a healthy life is minimal, but its deficiency could result in haywire, aggravating diseased conditions in the body. In this write-up, we shall discuss sunlight and vitamin D.
When it comes to detailing the causes of vitamin D deficiency, there are certainly a few obvious ones that need to be correlated with other clinical findings.

• Not enough exposure to the sun
  Getting less or no exposure to sunlight is probably the most common cause of vitamin D deficiency, especially for those who do not step out of the house more often. People staying at southern and northern latitudes, or those who keep their bodies covered at the time, could face the lack of this vitamin. The simple reason behind this is that the less your skin gets exposed to the sunlight, the fewer quantities of vitamin D your body will produce.
• The age and the skin shade
  The process of aging deems every element of health, including the absorption of vitamin D. It is found that people at an older age are not capable of absorbing the entire course of vitamin D. As a result, they suffer a deficiency of it. Also, dark skin shade or sunscreen application could lead to the hindrance of vitamin D absorption.
• Other reasons
  People suffering from skin pigmentation and those who stay in an environment with excessive air pollution could suffer Vitamin D deficiency. This is because pigmentation on the skin and pollution in the air exist as barriers to prevent the sunlight (UV rays) from getting absorbed into the skin.
  Moreover, it is essential to know that the natural source of getting vitamin D is nothing but exposure to sunlight. As per one study, 90-95% of the body’s vitamin D is produced from the skin under the sun’s influence. So now, let’s see how sunlight generates a vital amine (vitamin) in the human body.

How does our skin produce vitamin D from sunlight?
Our body, that is, our skin, is naturally fortified with the precursors (dehydrocholesterol) of vitamin D. When the skin contacts the sun’s ultraviolet rays, these precursors get converted into the pre-vitamin molecules called D3. These pre-vitamin molecules are then made to undergo a series of processes through the liver and kidney until they finally get transformed into 25-hydroxyvitamin D (Vitamin D). The active form of 25- hydroxyvitamin is 1,25-dihydroxyvitamin, which becomes available to the body for carrying out different bodily functions such as fixation or regulation of calcium and phosphorus in the bones and the circulating blood.

Let’s have a look at vitamin D synthesis in a step-by-step manner:

STEP 1: Sunlight interacting with the skin

The sunlight’s crucial entities interacting with the skin are ultraviolet B photons (290-315 mm). They break down the reserved stores of dehydrocholesterol (precursors of vitamin D) that naturally exist in the skin, resulting in pre-vitamin D3 in the epidermis.

STEP 2: Processing of pre-vitamin D3

Pre-vitamin D3 then undergoes a thermal isomerization process (a process that causes structural changes in a given molecule under thermal conditions), which leads to the formation of vitamin D or 25-hydroxyvitamin D. Vitamin D formed in this step is biologically inert. It requires to be processed further to be utilized by the body.

STEP 3: Processing of Vitamin D

The inactive form of vitamin D or 25-hydroxyvitamin D can go through several hydroxylations (introduction of hydroxyl groups) successively in the liver and the kidneys. After which the active form, i.e., 1,25-dihydroxyvitamin, is furnished to be used by the body.

Note: Complications or inefficiencies in any of these steps could make Vitamin D unavailable to the body even though enough exposure to sunlight is procured.

Less exposure to sun equals lower vitamin D levels
Less exposure to sunlight is directly related to vitamin D deficiency, which could initiate various health problems.
Vitamin D plays its role in absorbing the minerals such as calcium and phosphorus from food. These minerals are responsible for the excellent health of bones, teeth, and muscles. Under vitamin D deficiency, the bones often become soft and weak enough to withstand any pressure on them, resulting in frequent breaks or fractures. This condition could give rise to full-fledged bone disorders such as rickets or osteomalacia.
The dark side of Bright Sunlight!
Assuming sunlight to be consistently pleasant, soothing, and vitamin bestowing could be worrying too. Spending a limited span versus much exposure to the sun could turn out to be harmful to health.
These are the harmful effects of excessive exposure to the sun:

• Too much sunlight can cause wrinkling, thickening of the skin, tanning, and in adverse cases, sunburns. Such changes are caused due to DNA disruption or damage to the skin’s collagen from the harmful sun rays.
• At times, excessive sun exposure could lead to the weakening of skin’s immunity. This is because the harmful radiation from the sun results in the inactivation and the loss of epidermal Langerhans cells, which are an essential part of the skin’s immunity.
• Actinic Keratosis is when the skin turns rough, scaly, pink, red, or sometimes gray or brown. The disease can be a precancerous change on the skin, aroused from long-term exposure to sunlight.
• Chronic exposure to the skin since childhood or adulthood as part of the profession or a routine habit could even invite incidences such as skin carcinoma, which includes Basal cell carcinoma, Squamous cell carcinoma, and Melanoma.

Conclusion

Whether it’s sunlight or anything, exceeding limits could pose a potential threat to health. It’s important to know that our body needs only a little exposure to the sun, that is, for a few minutes every day, to make enough vitamin D. Also, one must know their skin types as sensitive skin might not require more exposure as sunlight could penetrate directly. However, a person with a darker skin shade would need to spend more time in the sun comparatively. Furthermore, there is no harm if the body makes more vitamin D from sunlight, but it’s essential to acknowledge the threshold when your skin starts showing unusual signs.

REFERENCES

1. Vitamin D Deficiency. Accessed at
   https://www.msdmanuals.com/en-in/home/disorders-of-nutrition/vitamins/vitamin-d-deficiency
2. Chang, S. W., & Lee, H. C. (2019). Vitamin D and health-The missing vitamin in humans. Pediatrics & Neonatology, 60(3), 237-244.
3. Wacker, M., & Holick, M. F. (2013). Sunlight and Vitamin D: A global perspective for health. Dermato-endocrinology, 5(1), 51–108. https://doi.org/10.4161/derm.24494
4. Holick MF. Defects in the synthesis and metabolism of vitamin D. Exp Clin Endocrinol Diabetes. 1995;103(4):219-27. doi: 10.1055/s-0029-1211354. PMID: 7584527.
5. How to get vitamin D from sunlight. Accessed at https://www.nhs.uk/live-well/healthy-body/how-to-get-vitamin-d-from-sunlight/
6. Acar, S., & Özkan, B. (2021). Vitamin D Metabolism. In Vitamin D. IntechOpen.