What's the hardest vitamin to get? A deep dive into Vitamin D and B12

December 29, 2025 •

4 min read

Worldwide, vitamin D inadequacy affects an estimated 1 billion people, making it a widespread public health concern. Yet, for specific populations like vegans, vitamin B12 poses an entirely different, and equally serious, challenge. So, what's the hardest vitamin to get, and does the answer depend on your lifestyle?

Quick Summary

Assessing the difficulty of acquiring certain nutrients reveals that both Vitamin D and B12 present unique obstacles. Vitamin D synthesis depends on adequate sunlight, while B12 is almost exclusively found in animal products, requiring targeted strategies for many.

Key Points

Vitamin D's unique challenge: The body's primary source is sunlight, not food, making adequate intake difficult for those with limited sun exposure due to location, season, or lifestyle.
Vitamin B12's dietary limitation: As it is found naturally almost exclusively in animal products, vegans and strict vegetarians must rely on fortified foods or supplements.
Absorption declines with age: Older adults are at increased risk for deficiencies in both Vitamin D and B12 due to reduced synthesis from sun exposure and decreased digestive absorption.
Lifestyle impacts matter: Factors like living far from the equator, having darker skin, and spending less time outdoors significantly affect Vitamin D levels, whereas dietary choices are the primary influence for B12 status.
Fortification is a vital tool: Many foods are fortified with Vitamin D and B12, offering a strategic way to increase intake for the general population and at-risk groups.
Proactive supplementation is key: For those with dietary restrictions or absorption issues, regular and reliable supplementation is necessary to prevent severe deficiencies and health complications.

Vitamin D: The Sunshine Problem

Often called the 'sunshine vitamin,' Vitamin D is unique because the body can synthesize it endogenously when the skin is exposed to ultraviolet B (UVB) radiation from the sun. However, a significant portion of the global population suffers from Vitamin D deficiency due to factors that limit this natural production. The reliance on a non-dietary source is its primary complication.

Factors Affecting Vitamin D Production and Absorption

Geographical location and season: People living farther from the equator experience less intense sunlight, especially during winter months, hindering Vitamin D synthesis. This seasonal fluctuation can cause levels to drop significantly.
Skin pigmentation: Melanin, the pigment that causes darker skin, acts as a natural sunscreen. Individuals with darker skin need significantly more sun exposure to produce the same amount of Vitamin D as those with lighter skin.
Sunscreen use and lifestyle: Sunscreen, while vital for skin cancer prevention, blocks the UVB rays necessary for vitamin D production. Modern lifestyles, which often involve spending most of the day indoors, also contribute to low sun exposure.
Age: The skin's ability to synthesize Vitamin D from sunlight decreases with age, putting older adults at a higher risk of deficiency.
Body fat: Since Vitamin D is fat-soluble, a higher level of body fat can sequester the vitamin, preventing it from circulating in the blood.
Malabsorption issues: Conditions like cystic fibrosis, Crohn's disease, and celiac disease can impair the small intestine's ability to absorb nutrients, including Vitamin D.

While some foods like fatty fish and fortified dairy products contain Vitamin D, the amounts are often too small to rely on diet alone for most people. For many, supplements are necessary to maintain adequate levels, especially during winter months.

Vitamin B12: The Dietary Dilemma

Vitamin B12 is essential for nerve function, DNA synthesis, and red blood cell formation. The major challenge with B12 is its natural source: it is found almost exclusively in animal products, including meat, fish, eggs, and dairy. It is not present in significant amounts in plants unless they are fortified.

Populations at High Risk for B12 Deficiency

Vegans and vegetarians: Individuals on a strict plant-based diet are at the highest risk of B12 deficiency because their diets lack natural B12 sources. Supplementation is not just recommended but is essential for optimal health for this group.
Older adults: As people age, their ability to absorb B12 from food declines. This is often due to reduced stomach acid and a deficiency of intrinsic factor, a protein needed for B12 absorption.
People with malabsorption disorders: Similar to Vitamin D, conditions affecting the digestive tract, such as Crohn's and celiac disease, can hinder B12 absorption.
Individuals with pernicious anemia: This autoimmune condition prevents the body from making intrinsic factor, making B12 absorption impossible without injections or high-dose oral supplements.

While fortified foods like cereals, plant milks, and nutritional yeast offer an alternative for those avoiding animal products, the amount can vary, and careful label-checking is required. The most reliable strategy for at-risk populations is regular supplementation.

Vitamin D vs. Vitamin B12: A Comparative Look


Factor	Vitamin D	Vitamin B12
Primary Source	Sunlight exposure	Animal products (meat, fish, dairy)
Dietary Challenge	Limited natural food sources; most food needs to be fortified	Exclusively found in animal products; problematic for vegans/vegetarians
Absorption Issues	Depends on sufficient sun exposure, age, skin tone, body fat, and liver/kidney health	Depends on adequate stomach acid and intrinsic factor, which declines with age
Geographic Impact	Significant; impacted by latitude and season	None; access depends on diet choices, not location
Supplementation	Often required, especially in winter or for those with limited sun exposure	Critical for vegans; often needed by older adults and those with malabsorption

Conclusion: The Final Verdict

There is no single hardest vitamin to get, as the answer is contingent on individual circumstances and physiological factors. For the global population as a whole, Vitamin D likely poses the most widespread challenge due to its unique synthesis requirements and our modern, indoor-centric lifestyles. Its deficiency is influenced by numerous external factors, from location to skin tone. However, for a specific dietary group—vegans and strict vegetarians—Vitamin B12 is unequivocally the hardest, as it is naturally absent from their diet and requires deliberate supplementation. For older adults, declining absorptive capacity makes B12 particularly difficult to obtain, regardless of diet. Therefore, understanding your personal risk factors and lifestyle is key to identifying which vitamin may be your biggest nutritional hurdle and how to overcome it effectively. More information on addressing nutritional inadequacies can be found on authoritative sites like the National Institutes of Health.(https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/)

A note on supplements

When diet and sunlight are not enough, supplements provide a reliable and effective way to manage levels of both Vitamin D and B12. It is important to choose high-quality supplements and follow dosage recommendations, as excessive intake can be harmful. Consulting a healthcare provider or a registered dietitian is the best way to determine your individual needs.

The importance of testing

For anyone concerned about their levels, blood testing is the most accurate way to determine if you have a deficiency. Unlike many vitamins, symptoms of B12 deficiency can take years to manifest, making proactive monitoring particularly important. Regular check-ups are especially crucial for at-risk groups, including older individuals and those on plant-based diets, to prevent long-term health complications.

Frequently Asked Questions

The answer depends on the individual. For the general population, Vitamin D is more challenging due to widespread lack of sun exposure. For vegans and strict vegetarians, B12 is the hardest because it is not found naturally in plant foods.

It is very difficult to obtain adequate Vitamin D from food alone. While some foods are fortified or naturally contain small amounts (fatty fish, fortified milk), they are often insufficient to meet the body's needs, especially with limited sun exposure.

Vegans need B12 supplements because the vitamin is only naturally found in animal products. Without supplementation or fortified foods, a vegan diet will not provide sufficient B12, potentially leading to serious health issues.

Symptoms of B12 deficiency can include fatigue, weakness, nerve damage (tingling/numbness), and mood changes. A deficiency can also lead to macrocytic anemia, causing large, dysfunctional red blood cells.

Risk factors for Vitamin D deficiency include limited sun exposure, darker skin, older age, obesity, and malabsorption disorders. People living in northern latitudes are also at a higher risk.

Yes, skin color significantly affects Vitamin D synthesis. The melanin in darker skin acts as a natural sunscreen, meaning individuals with more skin pigmentation require substantially more sun exposure to produce the same amount of Vitamin D.

Besides adequate, safe sun exposure, you can improve absorption by consuming dietary Vitamin D with healthy fats, as it is a fat-soluble vitamin. Some studies also show magnesium intake may help.