For years, we were told Vitamin D is the 'bone vitamin'. That's like saying your phone is just for making calls. Sure, it's technically true, but wildly incomplete.
Today, after working with thousands of people and watching the research evolve, I've watched this nutrient reveal itself as one of the most underrated players with many layers in human health.
The great Indian Vitamin D paradox
8 out of 10 Indians are vitamin D-deficient. We live in a tropical country with abundant sunshine. So what's going on?
When was the last time you sat in the sun for 20 minutes on purpose? We are an 'indoor species' now. Sitting by a window feels sunny, but glass blocks the UVB rays needed for D3 synthesis.
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Our brown skin is a double-edged sword. The melanin that protects us also filters out UV rays, so we need way more sun exposure than fair-skinned people. Add urban pollution scattering UVB, and you're left with a tiny window between 11 AM and 2 PM when D3 synthesis can happen. Miss it? You're running on empty.
D2 vs D3: The original charger vs the knockoff
Think of D2 (plant-derived) as that third-party cable you bought online. It works, kind of, sometimes. D3 is from animal products and sunlight. It's the original charger. Your body recognises it instantly and keeps you charged longer. That's why supplements use D3.
What low Vitamin D actually does
Your bones aren't static. They're constantly breaking down and rebuilding. When D3 is low, the rebuilding slows down while the breakdown keeps going. Over time, your bones hollow out from the inside. That's osteoporosis. That’s why fractures happen after small slips that shouldn’t have caused damage.
Beyond the bones
Here's what changed everything for me. Researchers found vitamin D receptors in almost every tissue. Brain, immune cells, heart, pancreas. Even cancer cells.
The body doesn't install reception systems for no reason. These receptors are saying, "We need vitamin D here too. Your muscles need it. Not just the gym ones. Your heart is a muscle. So are your lungs and intestines. Low D3 shows up as muscle pain, early fatigue, and that feeling of 'why am I exhausted after one flight of stairs?'
The depression connection
Today, we are facing a 'silent collision' of two global crises: 280 million people are battling depression, while over 1 billion are functionally vitamin D deficient. These aren't separate issues. Brain regions that regulate emotions all have vitamin D receptors.
Let me be clear. D3 deficiency isn't the only cause of depression. But if you're already dealing with low mood, irritability, or fatigue? Low D3 makes it worse. The COVID lockdowns showed us this. Being stuck indoors for months was definitely a factor in that mental health crisis.
Your immune system's volume knob
When you're sick, your body dials up your body's natural soldier cells to fight off the infection. But when your immune system goes rogue and starts attacking your own body, like in an autoimmune condition, Vitamin D steps in and dials down the inflammation. Between 2020 and 2024, we saw an explosion of research confirming this: Vitamin D does more than just 'boost' immunity; it also balances it.
And there's more. Low Vitamin D is linked to high blood pressure and heart disease. Though the connection is complex, the point is: your heart needs D3 to stay healthy.
During pregnancy, Vitamin D acts as a silent architect: It remodels your arteries so the placenta can actually feed your baby, helps your immune system accept the pregnancy instead of treating it like an invader, and prevents developmental issues that could affect your child's health long after birth.
What you need to know
- Should you start supplements as soon as you see fatigue? This can be caused by many things. Don't assume it's D3. Get a blood test first and consult a health professional.
- Beware of the 'false normal', some people take a monthly D3 supplement and get tested immediately after. (wait for at least 1.5 months)
How to take D3 supplement:
If you are taking pills/powder: Since these don't contain fat, take them with a meal or after it.
Liquid/Syrup: These often contain oil already, making them easier for the body to absorb.
Injections: These are usually reserved for severe deficiencies.
A note on dosage: Whether you take 1,000 IU daily or 60,000 IU weekly, follow a clinical health professional’s advice.
More is not always better
Vitamin D3 is stored in the body, and taking too much (toxicity) can have side effects.
Your body is an interconnected system, not a bunch of isolated parts. Likewise, Vitamin D supports your muscles, your immunity, your energy levels, and how your brain functions.
The evidence is clear: vitamin D deserves your attention and awareness. So, testing, understanding your levels, and supplementing wisely is the key.
The opinions expressed in this article are those of the author and do not purport to reflect the opinions or views of THE WEEK.