Fatigue, Brain Fog, Weak Bones — Could Vitamin D3 and B12 Deficiency Be the Reason Most Indians Feel This Way?

By Kuerzen Research Team | Kuerzen Biosolutions Pvt. Ltd. | FSSAI Certified

You slept eight hours last night. You are not particularly stressed. You eat reasonably well. And yet — you wake up tired, drag yourself through the afternoon in a fog, and wonder why your knees and back ache more than they should at your age. You put it down to a busy life, bad posture, or simply getting older. Most Indians do.
But what if it is none of those things?
A pan-India diagnostic study by Metropolis Healthcare, conducted across nearly 1.5 million samples over three years, found that 75% of Indians show alarming levels of vitamin deficiency. A viral social media post in 2025 called for a "polio-like national drive" to tackle Vitamin D and B12 deficiencies across India — and the response was overwhelming. Millions of Indians replied with a single sentiment: this is me. The symptoms are everywhere. The awareness is not. And for a country that has more sunshine than almost anywhere else on earth, the scale of India's Vitamin D deficiency is one of the most striking public health paradoxes of modern times.

Why Is India Deficient in Vitamins Despite All That Sunshine?

The assumption has always been that Indians could never be Vitamin D deficient. The sun blazes for most of the year. Surely that is enough? As it turns out, no — and understanding why reveals a great deal about how modern Indian life has quietly eroded one of our most important nutritional foundations. Vitamin D is not obtained primarily from food. The body synthesises it in the skin when UVB rays from sunlight make contact with bare skin. The problem is that most urban Indians never actually expose their skin to midday sun. Office workers commute in vehicles, work under artificial light for eight to ten hours, and return home after sunset. Those who do step out often use sunscreen, full-sleeve clothing, or deliberately avoid direct sunlight for cultural or cosmetic reasons. The result is that India — one of the sunniest nations on the planet — has a Vitamin D deficiency rate that is now being described as an epidemic. Vitamin D deficiency affects 70% or more of urban Indian adults, making it one of the six most clinically significant nutrient deficiencies in the country, according to a Lancet analysis published in 2024.

What Vitamin D3 Actually Does — and What Happens When You Don't Have Enough

Vitamin D3 is not merely a "bone vitamin." It is a hormone precursor that influences over 200 biological processes in the human body, from immune regulation to muscle function to mood. This is why its deficiency produces such a broad range of symptoms — symptoms that are easy to dismiss individually but tell a clear story together. When Vitamin D3 levels fall below optimal range, the first signals are fatigue and muscle weakness — not dramatic, just a persistent, low-level exhaustion that does not respond to sleep. Bone and joint pain follows, particularly in the lower back, knees, and hips. Because Vitamin D3 regulates calcium absorption in the gut, inadequate D3 means inadequate calcium reaching the bones regardless of how much dairy you consume — leading to reduced bone mineral density over time. Mood disturbances, including low motivation and mild depression, are also well-documented consequences of Vitamin D3 deficiency, as D3 receptors are present throughout the brain and influence serotonin production. A peer-reviewed study published in PMC examining urban and rural populations across Pune found that deficient Vitamin D3 levels were consistently observed across all demographic groups, with findings pointing to a trend of deficient Vitamin D3 levels across different Indian populations regardless of income or geography. The implications are significant — this is not a problem confined to the elderly or the poor. It is widespread, democratic, and largely undiagnosed.

The B12 Problem — India's Vegetarian Population Is Especially Vulnerable

Vitamin B12 is where India's deficiency crisis takes on a distinctly Indian character. Unlike Vitamin D3, B12 cannot be synthesised by the body at all — it must come entirely from diet. And the primary dietary sources of B12 are animal products: meat, fish, eggs, and dairy. India has the world's largest vegetarian population. For hundreds of millions of Indians who eat little or no meat, B12 deficiency is not a risk — it is almost an inevitability without active supplementation. A comprehensive Metropolis Healthcare study across India found that 21% of all samples tested were deficient in Vitamin B12, with deficiency rates increasing with age and more pronounced in vegetarian populations. The symptoms of B12 deficiency are insidious because they develop so gradually. 
Early signs include persistent fatigue, tingling or numbness in the hands and feet, a brain fog that makes concentration difficult, and a general emotional flatness. As deficiency deepens, neurological symptoms emerge — memory difficulties, balance problems, and in severe, long-standing cases, potentially irreversible nerve damage. Vitamin B12 regulates the functions of the brain and nervous system and plays a critical role in blood formation. Long-term deficiency has been associated with increased risk of cardiovascular events including heart attack and stroke. What makes this particularly problematic is that many Indians living with B12 deficiency have no idea it is happening. The symptoms overlap so completely with stress, overwork, and ageing that millions of people are quietly managing a nutritional gap they have never been tested for.

Why D3 and B12 Almost Always Appear Together

These two deficiencies are frequently discussed separately, but in practice they very often occur together in the same individual — and when they do, their combined effect on energy, cognition, and physical wellbeing is substantially worse than either alone. Both Vitamin D3 and B12 play critical roles in energy metabolism. D3 regulates mitochondrial function — the process by which cells convert nutrients into usable energy. B12 is essential for the production of red blood cells, which carry oxygen to every tissue in the body. When both are deficient simultaneously, the body is operating with compromised energy production at the cellular level and reduced oxygen delivery to the tissues — producing a fatigue that is genuinely debilitating for many individuals, not merely inconvenient. The bone-brain-energy triad that results from combined D3 and B12 deficiency is why the Metropolis study found symptoms clustering so consistently: weak bones from D3 deficiency, cognitive fog from B12 deficiency, and profound fatigue from both. Addressing one without the other provides only partial relief. This is the clinical rationale for the combined D3+B12 supplementation approach, which research has shown to produce better outcomes than supplementing either nutrient in isolation.

Who Is Most at Risk in India — Are You in This Group?

While Vitamin D3 and B12 deficiency affects Indians broadly, certain groups face substantially higher risk:
Urban professionals who spend most of their day indoors face elevated D3 risk. Vegetarians and vegans face the highest B12 risk given the near-complete absence of B12 from plant-based diets. Older adults face both — D3 skin synthesis becomes less efficient with age, and B12 absorption decreases as stomach acid production declines. Women of reproductive age face compounded risk from the iron-D3-B12 interaction. Delhi NCR residents face particular vulnerability due to indoor urban lifestyles combined with limited dietary diversity. 
Children and adolescents — one in five Indians estimated to be Vitamin D deficient, with 46% of children aged 0–10 suffering from rickets, a bone-softening condition that is entirely preventable with adequate D3.

What the Research Says About Correcting These Deficiencies

The good news is that both deficiencies are highly correctable once identified. For Vitamin D3, studies demonstrate that restoring levels to the optimal range of 40–60 ng/mL produces measurable improvements in muscle strength, mood, immune function, and fatigue within eight to twelve weeks of consistent supplementation. A key finding from recent research is that Vitamin D3 is significantly more effective when taken alongside Vitamin K2, which ensures calcium is directed to bones rather than deposited in soft tissue and arteries — an important safety consideration for long-term D3 supplementation. For Vitamin B12, liquid supplementation has been shown in clinical research to produce faster and more reliable absorption than tablet forms in individuals with compromised gut absorption — which is common in older adults and those with digestive sensitivities. B12 levels typically begin improving within four to eight weeks of daily liquid supplementation, with neurological symptoms improving over a longer three to six month period with consistent use.

What Can Help?

For Indians looking to maintain healthy Vitamin D3 and B12 levels conveniently, Kuerzen's DB12 — Vitamin D3 + B12 Liquid Supplement   is formulated for daily maintenance. Each 1ml serving delivers 600 IU of Vitamin D3 alongside 2.2mcg of B12 in liquid form — chosen for superior absorption compared to tablet formats. Note: If you have a confirmed deficiency, higher correction doses may be needed under medical guidance. DB12 is designed for maintenance once levels are restored. Each pack of two 30ml bottles provides 60 servings of consistent daily supplementation. Kuerzen's DB12 is FSSAI-certified, GMP-manufactured at Kuerzen Biosolutions Pvt. Ltd. in Greater Noida, ensuring every ingredient is present at a clinically meaningful dose. It is suitable for vegetarians, children above five years, working adults, and senior citizens — covering the full spectrum of Indians most affected by these deficiencies.

Frequently Asked Questions

What are the symptoms of Vitamin D3 deficiency in India?

Persistent fatigue that does not improve with sleep, muscle weakness, bone and joint pain (particularly in the lower back and knees), frequent infections, low mood, and hair loss. A simple blood test measuring serum 25-hydroxyvitamin D levels confirms the diagnosis, with levels below 20 ng/mL indicating deficiency.

What are the symptoms of Vitamin B12 deficiency?

Persistent fatigue, brain fog, difficulty concentrating, tingling or numbness in the hands and feet, mood disturbances, and a pale or yellowish complexion. In more advanced deficiency, memory difficulties and balance problems emerge.

Can vegetarians get enough Vitamin B12 from their diet?

It is very difficult without either fortified foods or supplementation. Vitamin B12 occurs naturally only in animal products. While dairy contains small amounts, it is often not sufficient — especially for those with digestive issues. Regular supplementation is the most reliable solution for vegetarians.

Is it safe to take Vitamin D3 and B12 together?

Yes — Vitamin D3 and Vitamin B12 have no known adverse interactions and are commonly prescribed together in clinical practice. Recent clinical evidence, including a multicenter randomized controlled trial titled “Effects of a Novel Dispersible Supplement Containing 2500 IU of Vitamin D and 1000 µg of B12”, supports the benefit of combined supplementation. The study demonstrated that patients receiving both nutrients together achieved higher serum levels and better correction of deficiencies compared to those taking the vitamins separately. Kuerzen's DB12 formulation is designed for safe daily use within clinically studied dose ranges.

How long does it take to recover from Vitamin D3 and B12 deficiency?

Recovery varies. For D3, most notice improvements within 6–8 weeks of daily supplementation. Bone density improvements take 6–12 months. For B12, energy and mood typically improve within 4–6 weeks, while neurological symptoms may take 3–6 months to fully resolve.

The Bottom Line

Fatigue, brain fog, and weak bones are not inevitable features of modern Indian life, even though millions of Indians have quietly accepted them as such. They are frequently the signature of two correctable nutritional deficiencies — Vitamin D3 and B12 — that affect the majority of Indians and are among the easiest deficiency states to address with consistent daily supplementation. India has the sunshine. What it has lacked is awareness. That is beginning to change — and the first step is simply knowing what to look for and getting tested. Because tiredness was never meant to be your normal
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Key References

[1] Metropolis Healthcare. Pan-India Vitamin D, B12 and B9 Deficiency Study across 1,496,683 samples. https://www.metropolisindia.com/blog/nutrition/7-out-of-every-10-indians-are-vitamin-deficient-metropolis-study

[2] Prevalence of deficiencies of serum Vitamin D3 and Vitamin B12 among urban and rural population in and around Pune, India. PMC. 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12088579/

[3] Vitamin D and B12 deficiencies: A growing public health concern in India. Business Standard. 2025. https://www.business-standard.com/health/vitamin-b12-d-deficiency-india-silent-epidemic-risks-causes-125080700963_1.html

[4] Vitamin K2 and Vitamin D3 co-supplementation for bone and cardiovascular health. Journal of the American College of Nutrition. 2017. https://pubmed.ncbi.nlm.nih.gov/28922729/

[5] Impact Guru. Nutrient Deficiency in India — Complete Guide 2026. https://www.impactguru.com/info/nutrient-deficiency-in-india-complete-guide/

[6] NFHS-5. National Family Health Survey India 2019–21. Anaemia and nutritional deficiency data. http://rchiips.org/nfhs/NFHS-5Reports/NFHS-5_INDIA_REPORT.pdf