Recently, it has been published that a large majority of the Chilean population has insufficient levels of vitamin D, which has even led to the suggestion of enriching foods such as flour to try to correct this population-wide deficiency. However, the problem goes much further than a simple nutritional deficiency.

Today we know that vitamin D does not act solely as a traditional vitamin. In reality, it functions as a prohormone with systemic effects capable of influencing genetic functions, immunity, muscle health, energy metabolism, and even inflammatory balance. Its biological impact is so broad that many experts consider it insufficient to continue treating it only as a nutrient associated with calcium and bones.

In this context, a key question arises: are all forms of vitamin D the same? Although they are often used as synonyms, there are important differences between vitamin D2 and vitamin D3 in terms of origin, absorption, stability, and biological efficacy.

D3 is obtained by the body when the skin is exposed to UVB ultraviolet rays, which produces a transformation of the molecule 7-dehydrocholesterol. Neither form is active on its own. Both must be transformed in the liver and kidneys to "activate" and bind to cellular receptors.

On the other hand, Vitamin D:

Vitamin D acts on almost every organ in the body.

1. Bone and Mineral Health, controlling calcium and phosphorus homeostasis. This is the best-known function, as an adequate concentration prevents osteoporosis or rickets in children.
2. Immune System Modulator, stimulating macrophages and lymphocytes to fight viruses and bacteria. It also helps prevent the immune system from attacking the body itself (autoimmune diseases).
3. Muscle Function, there are vitamin D receptors directly in muscle cells. Its action is to improve contraction strength and balance, which is key to preventing falls in older people.
4. Brain Health and Mood, as it participates in the synthesis of serotonin and protects neurons from oxidative stress, directly influencing the prevention of seasonal depression and cognitive decline.

Although both forms can prevent diseases due to extreme deficiency, Vitamin D3 is the tool of choice in modern clinical nutrition due to its metabolic superiority. It is recommended to maintain blood levels between 30 and 50 ng/mL, ideally accompanying the supplementation with Vitamin K2 and Magnesium to optimize its function.

The body does not distinguish between a D3 molecule from sheep's wool (supplement) and one produced by your own skin. Both reach the liver and are converted into the same active metabolite.

1. Its availability does not depend on the weather, latitude, or the use of sunscreen.
2. It is possible to know exactly how many International Units (IU) are being ingested.
3. Supplements or fortified foods may contain excipients, such as low-quality refined oils (olive or coconut oil are recommended), colorants, stabilizers, cellulose capsules, or others.
4. Vitamin D from supplements enters via the intestine through chylomicrons (small fat transporters), which creates a faster peak but also a slightly faster elimination if there is no adequate fat base, so it is recommended to take them with a meal containing fat.
5. Humans are not evolutionarily equipped to obtain more than 10% of their Vit. D from food. 90% must be obtained from the sun or supplements.
6. One egg provides 40 IU of Vit. D, so you would have to eat at least 20 per day. 100g of wild salmon provides 600 IU, so you would need to eat it every day, with the increased risk of heavy metals.
7. Many fortified foods provide 100 IU per serving, so it is necessary to read the labels.
8. In obesity, Vitamin D gets trapped in fat tissue and does not reach the blood, which is why D3 is the only form capable of overcoming fat tissue resistance to normalize serum levels.
9. Although official recommendations suggest 800 IU, there is scientific documentation suggesting between 2,000 and 4,000 IU daily.

For bone to remain healthy, several nutrients are required working as a team. D3 alone is not enough, nor is calcium alone.

The function of D3 is to absorb calcium from the intestine and transport it into the blood. Without D3, only 10% to 15% of dietary calcium is absorbed.

Vitamin K2, in its MK7 form, activates osteocalcin, which fixes calcium in the bone, preventing its deposition in the arteries (suggested dose 100 to 200 mcg daily).

Magnesium is an essential cofactor for converting Vit. D3 into its active form (300 to 400 mg of magnesium bisglycinate or citrate is suggested).

Bone is approximately 30% collagen, which provides flexibility and constitutes a mineral deposition base (hydrolyzed type 1 collagen is suggested).

Vitamin C participates in collagen formation. It provides flexibility. Without Vit. C, the body cannot hydroxylate proline and lysine to form stable collagen fibers. A bone low in Vit. C is brittle (1g daily is suggested, divided into 2 to 3 daily doses).

The current trend is to prioritize calcium intake through food rather than supplements. In the case of supplementation, calcium citrate is recommended. You should never take calcium alone.

Zinc activates osteoblasts, which are bone-formers and facilitators of bone turnover. It is necessary for the production of the enzyme alkaline phosphatase, which is fundamental for depositing minerals into bone (10 to 15 mg daily, taken away from meals, is suggested). It should be accompanied by 1 mg of copper to prevent the zinc from depleting it.

Important: Bone only absorbs nutrients if it receives the message that it "needs to be strong." Walking, weightlifting, or resistance exercises are the stimulus necessary for the supplementation to work.

Current evidence indicates that vitamin D3 continues to be the most efficient form for elevating and maintaining adequate vitamin D levels in the body. Its greater potency, stability, and prolonged half-life allow for a better clinical response and more practical dosing, especially in supplementation strategies and nutritional recommendations.

While vitamin D2 may be a valid alternative in vegan formulas or certain specific contexts, D3 continues to stand out for its greater efficacy in optimizing 25(OH)D levels and promoting a better physiological response according to available scientific evidence.

Vegetology / NMR Analysis: Nuclear Magnetic Resonance (NMR) studies confirm that Vitamin D3 extracted from lichen is chemically identical to that synthesized in human skin and that derived from lanolin. There is no chemical "signature" that the body uses to distinguish the origin once the molecule is purified.

Holick, M. F. (2007). "Vitamin D deficiency". New England Journal of Medicine. This fundamental study explains how vitamin D3 (cholecalciferol) is the "native" natural form for primates and humans, unlike D2, which is a fungal analogue.

Haddad, J. G., et al. (1993). "Human serum binding capacity and affinity for 25-hydroxyvitamin D3 and D2". Journal of Clinical Investigation.

NIH (National Institutes of Health): Vitamin D Health Professional Fact Sheet (Updated 2024). This is the best source for seeing the differences in absorption between D2 and D3 in food.

The Endocrine Society Clinical Practice Guidelines: For dosing protocols and safety in the use of "industrial" vitamin D (supplements).

PubMed ID: 22552031: Meta-analysis on the superiority of D3 over D2.