A 2017 study in the American Journal of Clinical Nutrition found that 92% of long-term vegans had inadequate B12 intake. Not deficient — inadequate. That gap between “not sick yet” and “fully nourished” is where most plant-based eaters live. This article walks through the five nutrients that consistently test low in vegan populations, explains why they matter, and gives specific, evidence-based strategies to close each gap.
This is not medical advice — consult a licensed healthcare provider before making changes to your diet or supplement regimen.
Vitamin B12: The Non-Negotiable Gap
B12 is the most well-documented deficiency in vegan diets. It’s not produced by plants, fungi, or animals — it’s synthesized by bacteria in soil and water. Modern sanitation and industrial farming have eliminated the soil exposure that historically provided B12. No plant food naturally contains reliable amounts.
The consequences of low B12 are neurological: numbness, memory issues, fatigue, and irreversible nerve damage if left untreated for years. A 2014 review in Nutrients found that vegans have B12 intakes averaging 0.4–0.7 mcg/day — roughly 15–25% of the recommended 2.4 mcg/day.
What the evidence says about supplementation
Fortified foods (nutritional yeast, plant milks, breakfast cereals) can help, but they’re inconsistent. One brand of almond milk might have 1 mcg per serving; another might have none. The Oregon State University Linus Pauling Institute recommends that adults over 50 — and all vegans — take a supplement providing at least 25–100 mcg daily of cyanocobalamin, the most stable and studied form.
The Deva Vegan B12 sublingual tablet (1000 mcg, $12 per 90-count bottle) is a reliable option. Garden of Life mykind Organics B12 Spray (500 mcg per spray, $16) works for people who dislike swallowing pills. Both use cyanocobalamin, not methylcobalamin — the methyl form breaks down faster in storage and has weaker evidence for absorption.
Why you shouldn’t rely on food alone
Even heavy consumption of fortified foods rarely hits the 2.4 mcg target consistently. A single tablespoon of Bragg Nutritional Yeast provides 4 mcg — but that’s only if you eat it daily. Most people don’t. Supplementation is the only reliable method.
Iron: Absorption Is the Real Problem
Vegans actually consume more iron than omnivores on average — about 1.5–2x more, per a 2018 meta-analysis in Critical Reviews in Food Science and Nutrition. The issue is form. Plant foods contain non-heme iron, which has an absorption rate of 2–20% depending on what else is in the meal. Heme iron from animal products absorbs at 15–35%.
This means a vegan eating 20 mg of iron daily might absorb less than an omnivore eating 12 mg. The practical result: vegans have lower ferritin levels (stored iron) than non-vegans, especially premenopausal women.
How to double non-heme iron absorption
- Pair iron with vitamin C. Adding a squeeze of lemon to lentil soup or eating strawberries with oatmeal increases absorption 3–6x. A 2026 study in the Journal of Nutrition found that 50 mg of vitamin C (half an orange) raised non-heme iron absorption from 5% to 14%.
- Avoid inhibitors at the same meal. Tea, coffee, and calcium supplements block iron absorption. Drink tea between meals, not with them. Wait 1 hour after eating before drinking coffee.
- Cook in cast iron. A 2018 study in Food Science & Nutrition found that cooking acidic foods (tomato sauce, chili) in cast iron added 1–3 mg of iron per 100 g serving.
The Garden of Life Vitamin Code Raw Iron (22 mg, $20) is a whole-food supplement that includes vitamin C and folate for better absorption. The Now Foods Iron (Ferrous Bisglycinate) (18 mg, $8) is gentler on the stomach than ferrous sulfate and doesn’t cause constipation as often.
Omega-3 Fatty Acids: The DHA Conversion Bottleneck
Plant-based omega-3s come as ALA (alpha-linolenic acid) from flaxseeds, chia seeds, and walnuts. The body converts ALA into EPA and DHA — the forms used by the brain, eyes, and cardiovascular system. The conversion rate is roughly 5–15% for EPA and 0.5–5% for DHA, per a 2015 review in Progress in Lipid Research.
This means a vegan eating 3 tablespoons of ground flaxseed (6 g ALA) might produce only 30–300 mg of DHA. The recommended intake for brain health is 250–500 mg DHA per day. The gap is significant.
Algae oil is the direct solution
Algae-based DHA supplements bypass the conversion bottleneck entirely. A 2026 study in Nutrients found that 200 mg/day of algal DHA raised blood DHA levels in vegans to the same range as omnivores eating fish twice weekly.
The Nordic Naturals Algae Omega (500 mg DHA + 250 mg EPA per 2 capsules, $35 per 60-count bottle) is the most studied option — it’s third-party tested by the International Fish Oil Standards (IFOS) program. The Deva Vegan DHA (200 mg DHA, $12) is a budget-friendly alternative that still uses algae oil.
When you might not need to supplement
If your diet includes 3+ tablespoons of ground flaxseed daily and you have no inflammatory conditions, your conversion may be adequate. But most people don’t eat that much. Pregnant women, people with depression, and those with dry eyes or joint pain should strongly consider algal DHA.
Iodine: The Forgotten Mineral
Iodine is almost entirely absent from the standard vegan diet. Sea vegetables contain it, but levels vary wildly — 1 gram of kelp can contain anywhere from 15 mcg to 2,800 mcg. Too little causes hypothyroidism; too much can suppress thyroid function just as severely.
A 2019 study in the European Journal of Clinical Nutrition found that 77% of vegans had urinary iodine concentrations below the WHO cutoff for adequate intake (100 mcg/L). The recommended daily intake for adults is 150 mcg.
How to get 150 mcg/day without guessing
- Iodized salt. 1/4 teaspoon (1.5 g) provides about 71 mcg. Use it in cooking and at the table. Most sea salt, kosher salt, and pink Himalayan salt contain no iodine — check the label.
- Supplement carefully. The Now Foods Potassium Iodide (225 mcg, $6 for 120 tablets) provides a safe, consistent dose. Cut the tablet in half to get ~112 mcg if you also use iodized salt. Do not exceed 500 mcg/day from supplements.
- Seaweed in moderation. A 5-gram serving of dulse flakes (available from Maine Coast Sea Vegetables) provides about 50–100 mcg — but test a small amount first to gauge your tolerance.
Important: If you have Hashimoto’s thyroiditis or any thyroid condition, consult your doctor before adding iodine. Excess iodine can trigger flares in susceptible people.
Calcium: It’s Not Just About Bones
Vegans typically consume 300–500 mg less calcium per day than omnivores, according to a 2026 systematic review in Osteoporosis International. The RDA for adults is 1,000 mg (1,200 mg for women over 50). Low calcium intake increases fracture risk — a 2026 EPIC-Oxford study found that vegans had a 43% higher fracture rate than meat-eaters, largely driven by lower calcium intake.
But calcium also regulates muscle contraction, nerve signaling, and blood clotting. A chronic deficit doesn’t just affect bones.
Which plant milks actually deliver
| Brand | Calcium per 1 cup | Added vitamin D | Price per 64 oz |
|---|---|---|---|
| Silk Original Soymilk | 450 mg | Yes (120 IU) | $4.50 |
| Califia Farms Oat Barista Blend | 350 mg | No | $5.99 |
| Ripple Original Pea Milk | 440 mg | Yes (150 IU) | $5.49 |
| Blue Diamond Almond Breeze | 450 mg | Yes (100 IU) | $3.99 |
Shake the carton before pouring — calcium carbonate settles at the bottom. The Silk Original Soymilk is the most consistent option because it’s fortified with tricalcium phosphate, which has better absorption than calcium carbonate in some studies.
When to consider a supplement
If you don’t drink fortified plant milk (2 cups/day) and don’t eat calcium-set tofu (300 mg per 1/2 cup) or fortified orange juice (350 mg per cup), a supplement makes sense. The Kirkland Signature Calcium Citrate 500 mg ($18 for 240 tablets) is well-absorbed and doesn’t require stomach acid — take it with food. Avoid calcium carbonate if you take iron supplements simultaneously, as they compete for absorption.
The Bottom Line on Vegan Nutrient Gaps
The evidence is clear: a well-planned vegan diet can meet all nutrient needs, but it requires deliberate choices. B12 and DHA are the two nutrients most vegans should supplement without question. Iron, iodine, and calcium require attention to food choices and preparation methods. Skipping any of these five creates a measurable gap — not necessarily deficiency, but a gap that accumulates over years.
The good news is that the fixes are simple, cheap, and backed by decades of research. A single algae oil capsule and a B12 tablet cost about $0.30 per day. That’s less than the cost of a multivitamin — and more targeted.
As more long-term vegan health data emerges from cohorts like the Adventist Health Study and EPIC-Oxford, the picture is becoming clearer: nutrient gaps are preventable, not inevitable. The question isn’t whether a vegan diet can be complete. It’s whether the individual is willing to do the work to make it so.
Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making health-related decisions.
