What are the best sources of vitamin B12 and vitamin D?

Best Dietary Sources of Vitamin B12 and Vitamin D

For vitamin B12, prioritize animal-source foods including meat, fish (especially fatty fish like salmon), eggs, and dairy products; for those on plant-based diets, consume fortified foods or supplements as natural plant sources are unreliable. For vitamin D, prioritize fatty fish (5-25 μg/100g), fish liver oils (250 μg/100g), and fortified dairy products, recognizing that diet alone rarely meets the 15 μg/day requirement without supplementation.

Vitamin B12 Sources

Animal-Based Sources (Most Reliable)

The 2024 NICE guidelines clearly identify that diets excluding or low in animal-source foods are a primary risk factor for B12 deficiency 1. Animal products remain the gold standard:

• Meat and poultry - consistent, bioavailable sources
• Fish - particularly fatty fish varieties
• Eggs - readily accessible option
• Dairy products (milk, cheese, yogurt) - regular consumption maintains adequate levels

Plant-Based and Alternative Sources

For vegetarians and vegans, the evidence is more nuanced. While recent research identifies certain plant sources (algae, mushrooms, fermented vegetables, fermented beans) 2, a 2023 systematic review using sensitive mass spectrometry methods found highly variable B12 content 3:

• Nori seaweed: 1.03-2.68 μg per sheet (most reliable plant source)
• Shiitake mushrooms: 0.79-1.12 μg per 20g dry weight
• Fermented soy products: up to 20 μg per cup (highly variable)
• Hijiki seaweed: minimal content (3×10⁻³ μg/7g)

Critical caveat: Many plant sources contain B12 analogs that are biologically inactive in humans. The NICE guidelines emphasize that those on plant-based diets who don't consume fortified foods or supplements are at high risk 1.

Fortified Foods

Fortified foods are essential for plant-based diets - including fortified plant-based milk alternatives, breakfast cereals, and nutritional yeast. These provide reliable B12 when natural dietary sources are inadequate 3.

Vitamin D Sources

Natural Food Sources (Limited Options)

A 2022 comprehensive review identifies few naturally rich sources (>4 μg/100g) 4:

Excellent sources:

• Fish liver oils: 250 μg/100g (highest concentration)
• Fatty fish: 5-25 μg/100g (salmon, mackerel, sardines)
• Mushrooms (UV-exposed): 21.1-58.7 μg/100g
• Reindeer lichen: 87 μg/100g (not practical for most)

Moderate sources:

• Eggs: 1.3-2.9 μg/100g (primarily in yolk)
• Cheese: 1.3-2.9 μg/100g
• Beef liver: 1.3-2.9 μg/100g
• Dark chocolate: 4 μg/100g

Fortified Foods

Given that the European Food Safety Authority sets adequate intake at 15 μg/day, fortified foods are practically necessary 4, 5:

• Fortified milk and dairy products
• Fortified plant-based beverages
• Fortified breakfast cereals
• Fortified orange juice
• Fortified fat spreads

The 2024 Endocrine Society guideline notes that most multivitamins contain 800-1000 IU (20-25 μg) of vitamin D, which is cost-effective at $10-50 annually 6.

Supplementation Reality

Dietary sources alone rarely achieve adequate vitamin D intake - the evidence consistently shows that 15 μg/day is difficult to obtain through diet without fortified foods or supplements 4, 5. The Endocrine Society acknowledges this reality, noting vitamin D supplementation is inexpensive, accessible, and both animal-derived (lanolin) and vegan (lichen-based) D3 options exist 6.

Key Clinical Considerations

High-Risk Groups Requiring Attention

For B12 1:

• Vegans and strict vegetarians without supplementation
• Patients on metformin, H2-blockers, or proton pump inhibitors
• Those with atrophic gastritis, celiac disease, or autoimmune conditions
• Older adults with malabsorption

For Vitamin D 6:

• Those with limited sun exposure
• Darker skin pigmentation in northern latitudes
• Malabsorptive conditions
• Socioeconomically disadvantaged populations (higher baseline deficiency rates)

Practical Algorithm

1. Assess dietary pattern: Animal products consumed regularly? If yes, B12 likely adequate from diet; if no, fortified foods or supplements mandatory
2. Evaluate sun exposure and geography: Limited exposure or northern latitude? Vitamin D supplementation likely needed regardless of diet
3. Screen high-risk individuals: Use total serum B12 as first-line test (active B12 if indeterminate) 1, 7; check 25(OH)D levels in symptomatic or high-risk patients
4. Implement targeted intervention: Confirmed deficiency requires supplementation, not dietary modification alone 7, 8

Bottom line: While dietary optimization is important, both vitamins often require fortified foods or supplements to achieve adequate status, particularly for B12 in plant-based diets and vitamin D in most populations regardless of diet.