Vitamin D is often called the “sunshine vitamin,” yet deficiency of this essential nutrient is surprisingly common—even in countries like India that receive abundant sunlight throughout the year. Dr. Arun Karthik highlights this paradox and explains why Vitamin D deficiency has become a widespread but often overlooked public health concern. Despite living in sun-rich regions, many individuals remain deficient due to lifestyle, biological, and environmental factors. A nationwide analysis of over 2.2 million blood tests (2019–January 2025) by Metropolis Healthcare found 46.5 % of Indians were Vitamin D deficient Understanding why this happens, how it affects the body, and how it can be managed is crucial for long-term health, especially for people with chronic conditions such as diabetes.
Why Vitamin D Deficiency Occurs Despite Ample Sunlight
One of the most common assumptions is that living in a tropical country automatically protects people from Vitamin D deficiency. However, Dr. Arun Karthik explains that sunlight exposure alone does not guarantee adequate Vitamin D levels.
Several factors interfere with natural Vitamin D synthesis in the skin:
- Sunscreen use: While sunscreen is essential for protecting against skin cancer and premature aging, it significantly reduces the skin’s ability to synthesize Vitamin D.
- Skin color: Individuals with darker skin have higher melanin content, which naturally blocks UVB rays needed for Vitamin D production.
- Indoor lifestyle: Urbanization, desk jobs, screen-based work, and reduced outdoor activity mean people spend less time in direct sunlight.
- Clothing habits: Cultural and professional clothing that covers most of the body limits skin exposure to sunlight.
- Timing of sun exposure: Early morning or late evening sun, though pleasant, is less effective for Vitamin D synthesis compared to midday exposure.
As a result, Vitamin D deficiency is common across all age groups, including children, adults, and the elderly—often without obvious warning signs.
The Key Functions of Vitamin D in the Body
Dr. Arun Karthik emphasizes that Vitamin D is not just about bone health. It functions more like a hormone and plays a role in multiple physiological systems.
1. Immunity and Infection Resistance
Vitamin D plays a crucial role in regulating the immune system. It enhances the body’s innate immune response while preventing excessive inflammation. During the COVID-19 pandemic, Vitamin D gained global attention because individuals with sufficient levels were observed to have better immune resilience and recovery outcomes. Although Vitamin D is not a cure, maintaining optimal levels supports the body’s natural defense mechanisms against infections.
2. Bone and Muscle Health
Vitamin D enables proper absorption of calcium and phosphorus, which are essential for strong bones and teeth. Deficiency can lead to bone pain, muscle weakness, frequent fractures, and conditions such as osteomalacia in adults and rickets in children.
3. Heart Health
Dr. Arun Karthik notes that Vitamin D receptors are present in heart tissue and blood vessels. Adequate levels help regulate blood pressure, reduce inflammation, and support overall cardiovascular health. Low Vitamin D levels have been associated with an increased risk of hypertension and heart disease.
4. Diabetes and Insulin Sensitivity
Vitamin D plays a supportive role in insulin secretion and sensitivity. Deficiency can worsen insulin resistance, making blood sugar control more difficult. This is particularly important for individuals with Type 2 diabetes, where Vitamin D optimization may aid in better metabolic control. Patients visiting a diabetic centre in Coimbatore are increasingly being evaluated for Vitamin D levels as part of comprehensive diabetes care.
5. Cancer Risk and Cell Regulation
Vitamin D helps regulate cell growth and differentiation. Research suggests that adequate levels may reduce the risk of certain cancers by preventing abnormal cell proliferation, although ongoing studies continue to explore this relationship.
Non-Specific Symptoms: Why Deficiency Is Often Missed
One of the biggest challenges with Vitamin D deficiency is that its symptoms are vague and non-specific. Dr. Arun Karthik points out that many patients live with low levels for years without realizing it.
Common symptoms include:
- Persistent fatigue and low energy
- Muscle aches and joint pain
- Back pain
- Frequent infections
- Low mood or depressive symptoms
- Hair fall
- Poor wound healing
Because these symptoms overlap with stress, aging, or other medical conditions, Vitamin D deficiency often goes undiagnosed unless specifically tested.
Understanding the “Sweet Spot” for Vitamin D Levels
According to Dr. Arun Karthik, both deficiency and excess of Vitamin D can be harmful. This makes it important to understand the optimal reference range.
- Deficient: Below 20 ng/mL
- Insufficient: 20–30 ng/mL
- Optimal (Sweet Spot): 30–50 ng/mL
- Potentially Excessive: Above 100 ng/mL
The goal is to maintain Vitamin D within the optimal range, ensuring benefits without risking toxicity. Self-supplementation without medical guidance can sometimes lead to excessively high levels, which may cause complications such as kidney stones and calcium imbalance.
Sources of Vitamin D: Beyond Sunlight
Dr. Arun Karthik explains that relying solely on sunlight is often insufficient, especially for individuals with limited exposure or higher requirements.
Animal-Based Sources
- Fatty fish (salmon, mackerel, sardines)
- Egg yolk
- Liver
- Cod liver oil
- Fortified dairy products
Animal-based sources provide Vitamin D3, which is more efficiently absorbed by the body.
Plant-Based and Fortified Sources
- Fortified cereals
- Fortified plant-based milk (soy, almond)
- Mushrooms exposed to UV light
Plant-based sources typically provide Vitamin D2, which is less potent but still beneficial when consumed regularly.
Treatment Options: Tablets, Sachets, and Injections
When deficiency is confirmed through blood tests, Dr. Arun Karthik recommends individualized treatment based on severity, age, and underlying health conditions.
1. Oral Supplements
Vitamin D tablets or sachets are commonly prescribed for mild to moderate deficiency. These may be taken daily, weekly, or monthly depending on the dosage.
2. Injectable Vitamin D
In cases of severe deficiency, malabsorption, or poor compliance with oral medication, Vitamin D injections may be advised. These provide a rapid and sustained increase in Vitamin D levels.
3. Maintenance Therapy
Once optimal levels are achieved, lower-dose maintenance therapy is essential to prevent recurrence. This is particularly important for elderly individuals and people with chronic illnesses.
Vitamin D and Diabetes: A Special Consideration
For individuals with diabetes, maintaining adequate Vitamin D levels is especially important. Dr. Arun Karthik highlights that Vitamin D deficiency can worsen insulin resistance, increase inflammation, and negatively impact overall metabolic control.
Patients under the care of the best diabetologist in coimbatore are often advised regular screening for Vitamin D deficiency as part of a holistic diabetes management plan. Addressing Vitamin D deficiency alongside blood sugar control can improve energy levels, bone health, and overall quality of life.
Also Read: Crack Your HbA1c for Smarter Metabolic Fitness
Treating Vitamin D as a Long-Term Health Investment
Dr. Arun Karthik emphasizes that Vitamin D deficiency is not just a nutritional issue—it is a systemic health concern that affects immunity, metabolism, cardiovascular health, and long-term disease risk. Because the symptoms are subtle and easily ignored, proactive screening and guided supplementation are essential.
Rather than self-medicating, individuals should undergo proper testing, follow medical advice, and adopt a balanced approach that includes safe sun exposure, dietary sources, and supplementation when required. By treating Vitamin D optimization as a preventive health measure, individuals can significantly improve their overall well-being and reduce the risk of chronic complications