Vitamin D is a fat-soluble essential nutrient that can be produced by our body in sunlight. Vitamin D benefits and controls the functioning of critical body systems as the Immune system, Calcium absorption, and cell growth and signaling. Vitamin D can be ingested via some food sources and as a supplement. However, a prominent source of this Vitamin for humans is direct exposure to sunlight.
Additionally, Vitamin D from the sunlight has a higher residence time (more than 2 times) in our body as compared to that from the foods or supplements, thus making it more effective. Normally, 15-20 mins exposure of direct sunlight to our face, arms, and legs for about 2-3 times a week is sufficient for the required Vitamin D. There are two forms of Vitamin D:
Vitamin D3 – Cholecalciferol – It is produced in the epidermis and dermis layers of our skin when it is exposed to the sunlight. Additionally, food sources such as beef, oily fish, and egg yolk also provide with Vitamin D3.
Vitamin D2 – Ergocalciferol – It is naturally found in sun-exposed mushrooms and yeast and also artificially present in the supplements. Human beings are not capable of producing Vitamin D2.
Why do we need Vitamin D?
Vitamin D acts as a steroid hormone and it regulates the functioning of more than 30 types of cells that are present across our body:
Bone Density and Intestines absorption of nutrients – Vitamin D benefits and promotes the absorption of Calcium and Phosphate from the intestines, hence directly affecting the availability of bone minerals from our food to our body. Additionally, Vitamin D acts as a gatekeeper, allowing the absorption of Calcium from the blood to the bone making cells (osteoplasts).
Cell cycles – Vitamin D affects cell proliferation and differentiation for every tissue in the body. It regulates how genes are expressed (meaning whether they would be active or not) and signals transferred (communication of any command from one cell to another) across all body cells.
Immune System – Vitamin D benefits the innate immunity that fends off pathogens such as bacteria and viruses. Research states that Vitamin D inhibits the growth of cancerous cells and stops the proliferation of malignant cells. Vitamin D deficiency has been positively correlated with Colon, Prostrate, and Breast Cancer. It also has immunomodulatory properties, as it directs the functioning of killer immune T cells and memory immune cells. This
Parathyroid Glands – It directs the functioning of parathyroid glands towards the release of PTH – parathyroid hormones, which participate in Calcium absorption cycle.
Cardiovascular system – Vitamin D benefits the cardiovascular system through various handles. It helps to reduce blood pressure by removing excess PTH – parathyroid hormones, which contributes to hypertension. It also reduces inflammation in the body, which is related with reduced risk of heart diseases.
Pancreas – Vitamin D is involved in the functioning of pancreatic beta cells, which are responsible for insulin secretion. It also improves insulin sensitivity, thus reducing the risk of Di
Musclar Function – Vitamin D modulates muscle cell proliferation and differentiation, meaning it is able to regulate development of muscle tissues. It also affects muscle physiology by balancing hyperparathyroidism, which is related with muscle deformities.
Factors that influence the bioavailability or absorption of Vitamin D in our body
Vitamin D that comes from our diet or via skin generation is naturally inert. This means it requires further processing in the body to influence the body functions. There are two steps in which Vitamin D is made available to our body in a biologically active form:
Hydroxylation in the liver to make Calcidiol, which stays in the blood for 15-30 days. At this stage, it is still inert and requires further processing. This form of Vitamin D is used to measure the nutritional status during reporting.
Hydroxylation of Calcidiol in the kidneys to make Calcitriol, which is biologically active and transferred across all body parts. This form of Vitamin D regulates body organs and body systems.
Factors that affect the synthesis of Vitamin D from sunlight
Our skin synthesizes Vitamin D under direct exposure of the Ultra-Violet (UV) rays of the sunlight. The self-generation process of Vitamin D in the human body is influenced by:
Time of the day – Early morning (2 hours after the sunset) and late evening (2 hours before the sunset) timings are considered to be the ideal timings of sun exposure.
Season of the year – Cloudy days are almost ineffective, hence depend on direct exposure on a sunny day! Also, during winter times when sunlight is not strong enough will also lower Vitamin generation. One would require longer times under the sun in winters.
Latitude – Higher latitudes get negligible sunlight, hence lowering the production of Vitamin. People living in high latitudes need extended exposure to the Sun and should consume Vitamin D rich foods as part of their diet.
Skin color – Dark skin is less effective in Vitamin D production as the melanin (pigment responsible for dark skin color) inhibits absorption of UV radiation. One would need more time under the Sun on a weekly basis.
Health condition of skin – Patients suffering from skin disorders such as Psoriasis are unable to generate sufficient Vitamin D.
Age – Vitamin D generation from the sunlight reduces as we age, hence elderly (60+ years) need to spend more time under the Sun to produce
Others – High levels of pollution and an absence of outdoor activities reduce production of Vitamin D from sunlight.
Factors that affect the absorption and availability of Vitamin D
Since Vitamin D needs to be processed by the liver and the kidneys to become bioactive, any malfunctioning of these two organs will affect the availability of Vitamin D to the rest of the body.
Additionally, for dietary Vitamin D, its availability is also dependent on the health of our digestive system. For example, patients suffering from Crohn’s disease are also prone to Vitamin D deficiency.
Myths regarding Vitamin D from the Sun!
One should not spend hours under the Sun to produce Vitamin D. In fact, just 15-20 mins are enough for our fat cells to replenish the storage buffer of Vitamin D. After the body has generated required amounts, the synthesis process automatically shuts down, extra produced is excreted.
One should not expose themselves to the hot noon Sun on a regular basis! Noon sunlight is dense in infra-red rays and UV rays but the intensity of sunlight is so high that our skin may be prone to cancers if we spend extended hours on a regular basis. It is recommended that one should wear light coloured clothes to cover their skin in the hot summer sun and expose their body parts to morning and evening sun for required vitamin generation.
Sunlight during a cloudy day and in the shade areas is almost ineffective! This is because your body parts are not getting exposed to required UV rays in shaded times and areas. Hence, one should look for direct contact of the skin with sunlight to
Skin doesn’t need to be burnt to generate Vitamin D! Just a casual exposure of 15-20 mins of rising or setting Sun for 2-3 times a week is enough for your body. Hence, avoid the heat but get the required UV rays at
References
Vitamin D in health and disease
Vitamin D and Calcium – Systematic Review
Vitamin D – The sunshine Vitamin