vitamin D deficiency, vitamin B12 deficiency and iron deficiency anemia can each cause fatigue, poor concentration, irritability, and flat mood exactly the same cluster of symptoms we interpret as depression. No one is going to find evidence of depression through a blood test, but addressing a possible
deficiency is not a substitute for therapy. The value of the test lies in determining whether there is anything physical causing the symptoms, thus providing a basis for a more informed treatment plan.

Key takeaways

• Vitamin D, B12 and iron deficiencies share most of their early symptoms with depression:tiredness, low motivation, brain fog, low mood.
• All three are common in India. Vitamin D deficiency estimates in Indian adult studies range from roughly 50% to over 90%, B12 deficiency runs near 47% in the general population and higher in vegetarians, and 57% of Indian women aged 15–49 are anaemic.
• Ferritin falls before haemoglobin does, so a normal CBC can still sit on top of depleted iron stores.
• Evidence for supplementation improving mood is strongest in people who were genuinely deficient to begin with, and much weaker in people who were not.
• These are contributing factors to rule in or out, not explanations that replace a clinical assessment .

Why a nutrient deficiency can look like depression

Ask anyone to describe early signs of iron deficiency and they will describe feeling tired all the time, inability to focus, irritable, sleeping poorly, feeling like nothing is worthwhile. If you ask anyone to describe mild depression, you get the same list again.

This is the issue in its entirety. Symptoms are the raw data in a mental assessment, and when two very different problems have the same symptoms, symptoms are not going to help make a differential diagnosis. Your therapist can develop an accurate picture based on your
account but fail to consider your thyroid levels or your ferritin levels which might change the approach completely.

None of this takes away from the need for the psychological assessment. An individual could have low vitamin D and a case of depression and in many cases, the only answer is that
both of them are present and both are supporting each other. Tests exist to avoid you guessing about the part that you can measure.

Vitamin D: the marker that comes up most often in Indian blood work

Vitamin D is usually associated with bone health in most people’s minds. Not so commonly known is that receptors of vitamin D are distributed throughout the brain in areas controlling mood, motivation, and sleep and that vitamin D plays an active role in the synthesis of serotonin, dopamine, and norepinephrine. That’s the biochemical basis for why doctors started testing it in people complaining of low mood and fatigue.

What the research actually shows

The truth is a little bit more nuanced than the truth you can find on social media. Observational studies have shown time and again that patients with insufficient vitamin D have a greater number of depressive symptoms than individuals with sufficient vitamin D. The direction of causality here is unclear because depressed individuals spend less time outdoors and eat less regularly, both of which reduce vitamin D levels.The evidence from clinical trials has been inconclusive but it is becoming increasingly clear. In a 2024 meta-analysis of 31 randomised trials involving 24,189 patients, it was found that supplementation led to a modest decrease in the number of depressive symptoms, with a stronger effect observed in those patients that showed depressive symptoms compared to those without any. Previously conducted meta-analyses of the same trials in individuals with baseline sufficient vitamin D have found zero benefits from supplementation. When taken together, it all becomes clear: correction of a deficiency helps a little bit and supplementation in individuals without a deficiency helps almost nothing. That is why vitamin D should be tested rather than assumed.

Why deficiency is this common in a country with this much sun

India gets abundant sunlight and still reports some of the highest deficiency rates in the world.Meta analysis of South Asian data puts Indian prevalence around 67%, and Delhi NCR study found severe deficiency in 71% of urban residents against 20% in rural ones.The urbanrural gap tells you most of the story. Office hours indoors, commutes in covered vehicles, sunscreen, urban air pollution filtering UVB, and more melanin requiring longer exposure to synthesise the same amount of vitamin D. Add largely vegetarian diets with few naturally D-rich foods, and a city like Chennai produces deficiency at scale despite the weather.

What a low result actually means for you

In case your Vitamin D (25-OH) levels are low, the next steps to follow are quite normal: vitamin supplementation with a dosage prescribed by your doctor, some sun exposure, and retest after about three months. What this does not mean is that you had mood symptoms "because of a lack of vitamins". This means that the variable has been found and is now being corrected, thus making the rest of the variables easier to interpret.
If brain fog is your primary symptom instead of low mood, you can find information on vitamin D deficiency and brain fog elsewhere.

Vitamin B12 and folate: the vegetarian blind spot

B12 is only reliably available from animal sources, which makes deficiency close to structural in a country with this much vegetarianism. Research on vegetarian Indians has found subclinical B12 deficiency in roughly 70% of those studied, with estimates near 47% across the general Indian population.

B12 and folate both feed one-carbon metabolism, the pathway that produces the methyl groups used in neurotransmitter synthesis. When either runs low, the neurological and psychiatric symptoms can arrive well before the anaemia does: low mood, irritability, poor memory, tingling in hands or feet. In one North Indian tertiary care series of 259 B12-deficient patients, 60 presented with neuropsychiatric symptoms.

Worth knowing: B12 supplementation can partially correct the blood picture while nerve symptoms continue, and folate supplementation can mask a B12 deficiency on a routine blood count. Both are reasons to test the two together and to have a clinician read them together ,which is why Folate (B9) sits in the Deep Dive tier alongside the B12 already in Starter.

Iron and ferritin: why a normal haemoglobin still hides a problem

The lack of iron is the most prevalent form of malnutrition in India, and for women, it borders on being a default. According to NFHS-5 (2019-21), anaemia was prevalent in 57% of women aged 15-49, compared to 53% in the previous round.

Ferritin falls first

Your body protects circulating haemoglobin for as long as it can by drawing down stored iron.Ferritin reflects that store. So the sequence is: ferritin drops, symptoms begin, and haemoglobin drops last.

Which means a CBC can come back entirely normal in someone whose iron stores are nearly empty, and they get told their blood work is fine. Ferritin is the marker that catches it earlier, which is why it sits in the Iron Profile in the Deep Dive and Complete panels rather than relying on haemoglobin alone.

What the evidence supports, and what it doesn't

Fatigue: quite reasonable. In meta analyses of RCTs, there is sufficient evidence to suggest that iron deficiency without anaemia is a possible cause of fatigue, which is improved in women with low ferritin but normal haemoglobin level by supplementation.
Mood: actually inconclusive. Some case control studies report an association between low ferritin and depression, while a French RCT conducted on 198 women with low ferritin but normal haemoglobin level was able to raise ferritin levels without making a difference to the depression or anxiety scores. We prefer to say this to you than exaggerate it.
The justified stance: low ferritin may be considered to be a definite reason behind your fatigue,but not your mood and definitely not to be left untreated clinically.

Who should push this to the top of the list

• Women with heavy or long menstrual periods
• Anyone vegetarian or vegan without deliberate iron planning
• Postpartum women
• People who have been reliably tired for months despite adequate sleep
• Anyone told their haemoglobin was "borderline but fine" without ferritin being checked

What each marker tells you, at a glance

Vitamin D (25-OH)
Circulating vitamin D status.

Symptoms: Low mood, fatigue, poor sleep, aches.
TLHC tier: Starter and above.

Vitamin B12
B12 status.
Symptoms: Low mood, memory problems, tingling, fatigue.
TLHC tier: Starter and above.

Folate (B9)
Folate status; read alongside B12.
Symptoms: Low mood, irritability, fatigue.
TLHC tier: Deep Dive and above.

Haemoglobin / CBC
Current oxygen-carrying capacity.
Symptoms: Fatigue, breathlessness, pallor.
TLHC tier: Starter and above.

Ferritin + Serum Iron
Stored iron; falls before haemoglobin.
Symptoms: Fatigue, poor concentration, low motivation.
TLHC tier: Deep Dive and above.

What actually happens after a low result

A number on a report is not a plan. The sequence that makes it useful:

1. A clinician reads it in context. Every panel includes a 20-minute session with a psychologist, so the result is interpreted alongside what you're actually experiencing rather than handed to you as a PDF.

2. Correction, at a dose someone set for you. Deficiency doses are not maintenance doses, and self-dosing vitamin D from the internet is how people end up with a different problem.

3. A repeat test, usually at three months. Levels are the only way to confirm the correction worked.

4. The result goes into the therapy conversation. If you're seeing a therapist through Book a Couch, a flagged deficiency becomes context for the work rather than a disconnected finding.

Where these markers sit in the panels

Vitamin D, B12, haemoglobin and CBC are in Starter Check (₹1,499) the reasonable first pass if you haven't had blood work in over a year.

Folate and the full Iron Profile, including ferritin, begin at Deep Dive (₹2,999). If fatigue is your dominant symptom, or you're a woman with heavy periods, Deep Dive is the more sensible starting point, because Starter alone can miss depleted iron stores.

Sample collection is at home through Neuberg Diagnostics, and reports come back in 24 to 48 hours.

Sources

• Vitamin D supplementation and depression: dose–response meta-analysis of 31 RCTs (2024)
• Vitamin D supplementation to reduce depression in adults: meta-analysis of RCTs High prevalence of vitamin D deficiency among South Asian adults: systematic review and meta-analysis
• Vitamin D deficiency in urban and rural Delhi NCR
• Identification of vitamin B12 deficiency in vegetarian Indians, British Journal of Nutrition
• Vitamin B12 deficiency in northern India tertiary care: prevalence, risk factors, clinical characteristics
• NFHS-5 anaemia data, Ministry of Health and Family Welfare / PIB
• Iron deficiency without anaemia as a cause of fatigue: meta-analyses of RCTs andcross-sectional studies

Fatigue and low mood that hasn't shifted in months is worth checking properly. Book a BloodTest for Mental Health home collection across India, reports in 24 to 48 hours, and a20-minute session with a psychologist to read them with you.

Medical disclaimer: this article is for general information and is not a substitute for professional medical advice, diagnosis or treatment. Blood tests cannot diagnose depression, anxiety or any mental health condition. Do not start or change any supplement or medication based on this article. Always consult a qualified physician or mental health professional about your own results.