Vitamin D Deficiency

Dr. ANUPA BASNET

They say, “Sunshine is the best medicine,” but it is more than medicine—it is the very sustainer of life. From Hinduism to ancient Egypt, Japanese Shinto, and the civilizations of Greece and Rome, the Sun was revered as a deity because without sunlight there would be no photosynthesis, no rainfall, and no water cycle. It is essential for climate regulation and food production; without sunlight, there is no food. 

In medicine and nutrition, sunlight is vital for the synthesis of vitamin D, whose deficiency is now linked to a wide range of diseases, not just calcium and bone metabolism. Did you know vitamin D is called the “sunshine vitamin”?

There are two main forms—vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). D2 is produced when the plant sterol ergosterol is exposed to sunlight. D3 is formed in our skin when sunlight converts 7-dehydrocholesterol into vitamin D3.

The active form of vitamin D is 1,25-dihydroxycholecalciferol (calcitriol). Its activation requires both the liver and kidneys: the first hydroxylation occurs in the liver, and the second in the kidneys. The metabolism of vitamin D and its active form was first described in 1967.

Globally, about 1 billion people are vitamin D deficient. In India, the situation is particularly alarming. According to the ICMR, deficiency affects 70–100% of the population, and a large multi-city study found that 76% of Indians have below-desirable vitamin D levels. The highest deficiency is seen among young adults under 25. India remains one of the most vitamin D-deficient countries, along with parts of the Middle East (Saudi Arabia, Iran, Turkey) and North Africa.

Although India is a tropical, sun-rich country and the Middle East has a hot, arid climate, vitamin D deficiency is paradoxically widespread due to several factors:

1. Darker skin: Higher melanin levels act as a natural sunscreen, reducing the skin's ability to synthesize vitamin D from UVB rays.
2. Diet: A large proportion of Indians follow a vegetarian diet. Natural dietary sources of vitamin D, such as egg yolk, fatty fish, and liver, are consumed less frequently.
3. Lifestyle, cultural practices, and heat: In many Middle Eastern countries, clothing that covers most of the body, such as the hijab or abaya, limits skin exposure to sunlight. Extreme heat also keeps people indoors. Modern lifestyles further reduce sun exposure, with most government employees, teachers, doctors, office workers, and other professionals spending long hours indoors. Night-shift workers, especially in the IT sector, sleep during the day and receive very little sunlight.
4. Excessive sunscreen use: Frequent use of sunscreen, while important for preventing skin damage and skin cancer, can reduce the skin's production of vitamin D when it blocks UVB rays.
5. Certain medications: Since vitamin D is a fat-soluble vitamin, weight-loss drugs such as orlistat, as well as medications like phenytoin and prednisone, can interfere with its absorption or conversion to its active form.
6. Malabsorption disorders: Conditions that impair fat absorption, such as celiac disease, Crohn's disease, or other malabsorption syndromes, can lead to vitamin D deficiency.
7. Liver and kidney disease: Patients with chronic liver disease, chronic kidney disease (CKD), or kidney failure are at higher risk because vitamin D must be activated first in the liver and then in the kidneys.
8. Ageing: As people age, the skin becomes less efficient at producing vitamin D in response to sunlight, increasing the risk of deficiency.

Have you often heard people say that early morning is the best time for sun exposure? Or seen our elders basking in the morning sun to relieve bone pain or boost vitamin D? This raises an important question: Is that advice a myth?

The answer is partly yes. Early morning sunlight is excellent for setting our circadian rhythm and synchronising our body clock with nature. However, it is not the ideal time for vitamin D synthesis.

For the skin to produce vitamin D, it needs UVB rays, which are strongest when the sun is at its highest. The best time for vitamin D synthesis is between 10 a.m. and 1 p.m. During the early morning, the sun is too low in the sky, and much of the UVB radiation is filtered by the atmosphere.

How much sun exposure is enough?

The ideal duration depends on your skin colour, as melanin acts as a natural sunscreen.

• Fair skin: 10–15 minutes
• Olive or wheatish skin: 15–20 minutes
• Dark skin: 30–45 minutes

Exposing the face, arms, and legs without sunscreen for this duration is generally sufficient on most sunny days.

Why should you not ignore vitamin D deficiency?

Vitamin D deficiency can have far-reaching effects on health, including:

1. Bone disorders such as rickets in children and osteomalacia in adults.
2. Low calcium and phosphate levels, leading to poor bone mineralisation.
3. Muscle weakness, cramps, and spasms.
4. Higher risk of osteoporosis and fractures, even after minor falls.
5. Mood disorders, including depression.
6. In people with cancer, deficiency has been associated with more advanced disease and poorer survival in some studies.
7. In women, it has been linked to more severe PMS, irregular menstrual cycles, PCOS, reduced fertility, and adverse pregnancy outcomes.
8. Reduced immunity, increasing susceptibility to frequent infections such as coughs and colds.
9. It plays a role in insulin secretion and glucose metabolism, making it important for people with diabetes.
10. Vitamin D also supports thyroid function, muscle health, and immune regulation. While it has an indirect role in normal blood clotting through calcium metabolism, it is not a direct clotting factor.

Can you take vitamin D supplements on your own?

In the age of the internet and AI, many people self-medicate and overload themselves with supplements. Vitamin D should not be taken indiscriminately, as excessive intake can lead to toxicity.

Before starting supplements, get your serum vitamin D level checked.

• 30–50 ng/mL: Sufficient
• 20–29 ng/mL: Insufficient
• Below 20 ng/mL: Deficient and usually requires supplementation under a doctor's supervision.

Who should take vitamin D supplements?

According to the ICMR, regular outdoor activity and sensible sun exposure are the best ways to maintain adequate vitamin D levels. However, people with minimal sun exposure may require 400 IU daily, preferably after confirming deficiency or insufficiency through a blood test.

Supplementation is also recommended for those with low vitamin D levels who experience symptoms such as:

• Persistent bone or joint pain, especially back pain
• Muscle cramps or weakness
• Fatigue
• Mood changes

Recommended Daily Allowance (RDA)

• Infants and children: 200–400 IU/day
• Adolescents: 400 IU/day
• Pregnant and lactating women: 400–600 IU/day
• Adults with minimal sun exposure: 400 IU/day
• Adults 51–70 years: 400 IU/day
• Above 70 years: 600 IU/day

Vitamin D-rich foods

Along with adequate sunlight, include vitamin D-rich foods in your diet. Among natural sources, the richest are:

1. Sardines
2. Salmon
3. Tuna
4. Shrimp
5. Liver
6. Egg yolk
7. Fortified milk
8. Mushrooms (UV-exposed)
9. Cheese
10. Butter
11. Sunflower seeds