How to get vitamin D on a vegan diet

Vitamin D deficiency is one of the most widespread nutritional issues globally — and it affects people on all dietary patterns, not just plant-based ones. For vegans, the challenge is specific: the most concentrated dietary sources of vitamin D are animal products, and sunlight exposure is unreliable for much of the world's population for much of the year.

This post covers how vitamin D works, why sunlight is often insufficient, the difference between supplement forms, what food sources actually contribute, how much is needed, and when testing makes sense.

What Vitamin D Does in the Body

Vitamin D functions more like a hormone than a standard vitamin. Once synthesised or ingested, it is converted by the liver and kidneys into calcitriol — the active form — which regulates calcium and phosphorus absorption in the gut, supports bone mineralisation, and plays a role in immune function, muscle performance, and cell signalling.

Without adequate vitamin D, the intestine absorbs only around 10–15% of dietary calcium, compared to 30–40% with sufficient vitamin D levels, according to research published in the American Journal of Clinical Nutrition. This is why vitamin D and calcium are functionally inseparable: calcium intake means very little if vitamin D is deficient.

The consequences of sustained deficiency include reduced bone density, increased fracture risk, weakened immune response, and muscle weakness. Severe deficiency causes rickets in children and osteomalacia in adults — both conditions involving soft, structurally compromised bone. Subclinical deficiency — insufficient to reach the clinical threshold — is considerably more common and produces subtler symptoms, including fatigue and reduced resistance to infection.

Why Sunlight Alone Is Often Not Enough

The body synthesises vitamin D when ultraviolet B (UVB) radiation from sunlight converts 7-dehydrocholesterol in the skin to pre-vitamin D3. Under ideal conditions — midday sun, significant skin exposure, appropriate latitude, summer months — this process is highly efficient. Under real-world conditions for most people, it is not.

Latitude is the primary constraint. Above approximately 35° North or South, UVB radiation is too weak to trigger meaningful vitamin D synthesis for several months of the year. Cities including London, New York, Berlin, Toronto, and Chicago — all above 40°N — receive insufficient UVB for synthesis from approximately October through March, according to data from the National Institutes of Health. Even in equatorial regions, heavy clothing, indoor work patterns, air quality, and darker skin pigmentation (which requires longer exposure to produce equivalent synthesis) reduce effective production.

Skin pigmentation specifically deserves mention. Melanin absorbs UVB and reduces the rate of vitamin D synthesis. People with darker skin tones require significantly longer sun exposure to produce the same amount of vitamin D as those with lighter skin — a factor frequently underestimated in general guidance that treats sunlight as uniformly adequate.

Sunscreen with SPF 30 reduces vitamin D synthesis by approximately 97%, according to research published in Photochemistry and Photobiology. Incidental exposure — through a window — to the hands and face does not produce meaningful synthesis because glass filters out UVB entirely.

The practical conclusion: sunlight cannot be relied upon as a consistent vitamin D source for most people in most latitudes for significant portions of the year. Supplementation is not a backup strategy — for the majority of the global population, it is the primary strategy.

D2 vs D3: What the Difference Is and Why It Matters

Vitamin D supplements come in two forms: D2 (ergocalciferol) and D3 (cholecalciferol). For most of the history of supplementation, D2 was the standard vegan option — it is derived from UV-irradiated plant sterols. D3 was derived from lanolin (sheep's wool) and, therefore, is not suitable for vegans.

This distinction matters because D3 is more effective. Multiple meta-analyses, including a review published in the American Journal of Clinical Nutrition, have found that D3 raises and maintains serum 25-OH vitamin D levels more efficiently than D2 at equivalent doses. The difference is meaningful over the long term.

The vegan supplement landscape has changed substantially. Lichen-derived D3 is now widely available — lichen synthesises cholecalciferol in a form biochemically identical to the D3 produced by human skin and to lanolin-derived D3. Brands including Vitashine, Nordic Naturals Vegan D3, and Garden of Life produce lichen-derived D3 supplements. Vegans now have access to the more effective form without compromise.

Both D2 and lichen-derived D3 are effective options. For people who prefer D2 or cannot access lichen-derived D3, D2 supplementation at adequate doses does raise vitamin D levels — the efficiency difference is most relevant when comparing equivalent doses over extended periods.

Vitamin D in Food

Fortified Plant Milks and Foods

Most vitamin D in food comes from fortification rather than natural occurrence. Calcium-fortified plant milks — soy, oat, almond, pea — are commonly fortified with vitamin D2 or D3, typically providing 1–2.5 mcg (40–100 IU) per 100ml. A standard cup (240ml) contributes roughly 2.5–5 mcg. Fortified breakfast cereals vary considerably by brand. Checking labels is necessary since fortification levels are not standardised across manufacturers.

Mushrooms

Mushrooms exposed to UV light — either natural sunlight or artificial UV lamps during commercial production — synthesise vitamin D2. Maitake mushrooms exposed to UV light can provide a meaningful amount per serving; portobello mushrooms placed gill-side up in direct sunlight for several hours accumulate D2 as well. Standard commercially grown mushrooms kept in the dark contain negligible amounts.

[P] UV-treated mushrooms are increasingly available in some markets, and some products carry labelling indicating vitamin D content. However, levels vary considerably depending on UV exposure conditions, and mushrooms are not a substitute for supplementation in regions with limited sun exposure. They are a useful supplementary contributor when available, not a reliable primary source.

The Practical Limit of Food Sources

The aggregate contribution of vitamin D from plant-based food — even a well-constructed diet including fortified milks and UV-exposed mushrooms — typically falls well short of the recommended intake. Food sources can contribute meaningfully to daily totals but are not sufficient as a standalone strategy for most people.

How Much Vitamin D Do Vegans Need?

The NHS recommends 10 mcg (400 IU) of vitamin D daily for all adults, particularly during autumn and winter months. The Vegan Society recommends the same daily amount, with higher amounts potentially needed in winter or for individuals with limited sun exposure, darker skin, or consistent indoor routines.

Research from the Adventist Health Study-2 found that vegans who did not supplement both calcium and vitamin D had significantly higher bone fracture rates than those who did supplement both — a finding that makes vitamin D supplementation one of the more evidence-backed recommendations for people eating plant-based diets.

Some practitioners recommend higher doses — 25 mcg (1,000 IU) or more — particularly in winter or for those with an established deficiency. Vitamin D is fat-soluble, meaning it accumulates rather than being excreted. This makes dose selection more relevant than with water-soluble vitamins: moderately higher doses are safe and often more effective, but extremely high supplementation over extended periods carries risk. Reviewing intake relative to test results is more useful than supplementing with a fixed number without data.

Vitamin D and Fat Absorption

Vitamin D is fat-soluble. Absorption is significantly improved when supplements are taken with a meal containing dietary fat. A study published in the Journal of the Academy of Nutrition and Dietetics found that vitamin D absorption increased substantially when taken with the highest-fat meal of the day compared to a fat-free meal. Taking a supplement on an empty stomach or with a low-fat meal reduces the amount absorbed.

Practically: taking a vitamin D supplement alongside breakfast with nut butter, avocado, seeds, or any fat-containing food makes the supplement meaningfully more effective. This applies to both D2 and D3.

Calcium and Vitamin D Together

Calcium intake and vitamin D status are functionally linked. Dietary calcium can only be absorbed efficiently when vitamin D levels are adequate — and without sufficient calcium in the diet, optimising vitamin D makes less of a structural difference. The two nutrients require each other to perform their primary functions.

This interaction matters practically for bone health. Research from the Adventist Health Study-2, as well as findings from the Women's Health Initiative, indicate that combined calcium and vitamin D supplementation reduces fracture risk more effectively than either alone. For vegans, who are at statistically higher fracture risk when both are insufficient, monitoring both simultaneously is the more complete approach.

Getting Tested: The 25-OH Vitamin D Test

The only way to know whether vitamin D levels are adequate is a blood test. The test measures 25-hydroxyvitamin D (25-OH vitamin D), the main circulating form, and reflects the combined contribution of sunlight, food, and supplements.

Optimal levels are generally considered to be 50–125 nmol/L (20–50 ng/mL). Deficiency is defined as below 30 nmol/L; insufficiency as 30–50 nmol/L. Results in the insufficient range are common even in people who believe their diet and sun exposure are adequate.

Testing is particularly worth doing before increasing supplement dose, when symptoms of fatigue, bone pain, or frequent illness are present, and annually in people who live at higher latitudes or have low sun exposure. Supplementing without testing is not harmful at standard doses, but testing provides a clearer basis for deciding how much to take.

Frequently Asked Questions

Can vegans get enough vitamin D without supplements?

In practice, most cannot — at least not consistently year-round. Fortified foods contribute, and UV-treated mushrooms add some, but dietary sources alone rarely cover the full recommended intake. At latitudes above 35° North or South, sunlight synthesis is insufficient for several months each year. The Vegan Society and NHS both recommend supplementation, particularly from October through March in the UK and equivalent winter months elsewhere.

What is the best vitamin D supplement for vegans?

Lichen-derived D3 is the most effective vegan option, performing comparably to lanolin-derived D3 and more efficiently than D2 at equivalent doses over time. Available brands include Vitashine and others labelled as vegan D3. D2 remains a suitable alternative, particularly at higher doses. Both should be taken with a fat-containing meal to maximise absorption.

How much vitamin D do vegans need per day?

The NHS recommends 10 mcg (400 IU) daily for all adults, with supplementation especially important in autumn and winter. The Vegan Society recommends the same, noting that some individuals with limited sun exposure, darker skin, or consistent indoor routines may benefit from higher amounts. Testing 25-OH vitamin D levels provides a more personalised basis than a fixed dose for everyone.

Does sunlight give vegans enough vitamin D?

For part of the year and in some latitudes, yes — in others, no. Above approximately 35° North or South, UVB radiation is insufficient for meaningful skin synthesis for several months of the year. Darker skin requires longer exposure to produce equivalent amounts. Glass blocks UVB entirely, and sunscreen with SPF 30 reduces synthesis by around 97%. Sunlight exposure should be considered supplementary rather than the primary strategy for most people.

Are vitamin D and calcium related?

Yes — closely. Vitamin D is required for the gut to efficiently absorb calcium. Without adequate vitamin D, even a calcium-rich diet is absorbed at a significantly reduced rate. Combined insufficiency of both is associated with a higher risk of bone fractures, a finding documented in the Adventist Health Study-2, particularly among people following plant-based diets. Addressing both together produces better outcomes than focusing on either alone.

What This Adds Up To in Practice

Vitamin D deficiency is not a vegan-specific problem, but the dietary routes available to vegans are narrower than those for omnivores. Fortified plant milks and UV-treated mushrooms contribute, but they rarely cover the full requirement independently. Sunlight is geography- and season-dependent, making it unreliable as a consistent source.

Supplementation is the most reliable strategy — and lichen-derived D3, taken with a fat-containing meal, is now the most effective option available in vegan form. Testing 25-OH vitamin D levels at least once a year converts supplementation from a guess into an informed decision.

At The Vegan School, the connection between nutrient status and how food is prepared — including how fat-soluble vitamins interact with dietary fat in cooking — runs through the curriculum as practical knowledge rather than nutrition theory.