Nutrients & electrolytes
Also known as 25-hydroxyvitamin D, Calcidiol. Measured in ng/mL.
Vitamin D is measured as 25-hydroxyvitamin D, the circulating storage form, which reflects combined intake from sunlight, diet and supplements over the preceding weeks. It is not really a vitamin but a hormone precursor, and its receptors appear throughout the body, which is why deficiency presents so vaguely: fatigue, low mood, diffuse muscle aches, bone and joint pain, and more frequent minor infections. Its best-established role is in calcium absorption and bone health, where the evidence is strong. Claims beyond that domain are considerably weaker than popular coverage suggests. Deficiency is nonetheless genuinely widespread — including in sunny countries, where skin pigmentation, indoor work, clothing and air pollution all reduce the amount of vitamin D the skin actually produces.
Deficiency is widespread across Indian populations despite abundant sunlight.
Skin melanin, indoor work, clothing and particulate air pollution all reduce how much the skin actually synthesises.
Retesting sooner than eight to twelve weeks mostly measures the last dose rather than a new steady state.
High vitamin D almost always reflects supplementation rather than sun exposure, which is self-limiting. Sustained very high levels can raise blood calcium, causing nausea, excessive thirst, confusion and kidney stones. This is uncommon but is a real risk with unsupervised high-dose regimens, which are widely sold in India.
Low vitamin D impairs calcium absorption and, over time, bone mineralisation. Symptoms are non-specific and easily attributed to something else — persistent tiredness, aching legs and back, low mood, frequent minor illness. Deficiency is common enough that it is worth measuring rather than assuming either way.
| Band | Value |
|---|---|
| Deficient | < 20 ng/mL |
| Insufficient | 20 – 29 ng/mL |
| Sufficient | 30 – 100 ng/mL |
| Potentially toxic | > 100 ng/mLEssentially only reached through supplementation |
Laboratory intervals vary. Interpret with a physician.
Vitamin D deficiency is documented across Indian populations at high prevalence despite abundant sunlight. Higher melanin content requires substantially longer sun exposure to synthesise the same amount, and urban indoor working patterns, full-coverage clothing and particulate air pollution compound this. Peak Brain finds it low in a large majority of the people it tests.
Vitamin B12 is required for red blood cell formation, DNA synthesis and the maintenance of the myelin sheath around nerves.
Ferritin is the protein the body uses to store iron, and the amount circulating in blood is proportional to how much iron is held in reserve.
Deficiency is common and usually managed straightforwardly with a physician-directed repletion regimen and a retest. Do not self-prescribe high-dose vitamin D: the sachets widely available in India can cause toxicity when taken repeatedly without monitoring. Bone pain, recurrent fractures or muscle weakness need medical assessment.
Sunlight availability and vitamin D synthesis are not the same thing. Higher skin melanin requires several times longer exposure for equivalent production; indoor work removes most midday exposure; clothing covers the skin that would otherwise synthesise it; and urban particulate pollution attenuates the relevant UVB wavelengths. Deficiency alongside abundant sunshine is the norm, not a paradox.
Eight to twelve weeks. 25-hydroxyvitamin D has a half-life of roughly two to three weeks, so retesting sooner than about two months mostly measures the last dose rather than the new steady state.
Low-dose supplementation is generally low-risk, but the high-dose weekly and monthly regimens commonly sold in India are not, and without a baseline there is no way to judge either the dose or whether it worked. Testing costs little relative to months of guessing.
The programme
Peak Brain draws a full blood and urine panel at your home, has a licensed physician read every marker together rather than one at a time, and turns what they find into a ranked 90-day protocol with a retest at the end.
Authorship & review
Written by the Peak Brain clinical team. Assigned clinical reviewer: Dr. RS Pradhan, MD — review pending; this page has not yet been signed off.
Published . Last updated .
This page is general health information, not medical advice, diagnosis or treatment. Reference ranges vary between laboratories. Never delay or disregard advice from a qualified health professional because of something you read here. If you think you may have a medical emergency, call your local emergency number.