Vitamin D deficiency: why most supplements don't help

Vitamin D deficiency: much more common than you think

Vitamin D is not just a vitamin — it is a prohormone that influences the expression of more than a thousand genes. It regulates calcium absorption, supports immune system function, and plays a role in muscles, nerves, and metabolism. A deficiency is therefore not a minor nutritional gap, but a systemic hormonal deficiency.

The European Commission estimates that 40 to 50% of European adults have insufficient vitamin D — significantly more in northern countries and during winter. Yet, blood tests often show that many people who take supplements faithfully still have levels that are too low. The problem is almost never the supplement itself, but the absorption, conversion, and cofactors that most products ignore.

Why vitamin D is more complex than it seems

Vitamin D is fat-soluble. It requires dietary fat to be absorbed properly and must then undergo several conversion steps before it is biologically active. The form found in most supplements — cholecalciferol (D3) — is first converted in the liver to 25-hydroxyvitamin D and subsequently in the kidneys to the active form. Each step requires specific enzymes, cofactors, and a properly functioning organ.

Four reasons why regular vitamin D falls short

1. Too little fat during intake

Vitamin D needs fat to be absorbed. Taking it on an empty stomach or with a fat-free meal significantly reduces absorption. Research shows that taking it with the largest meal of the day increases absorption by up to 50%.

2. Impaired gut function

Inflammatory bowel diseases, celiac disease, dysbiosis, and low bile production all hinder the absorption of fat-soluble vitamins. Anyone with digestive issues is at a clearly higher risk of deficiency, even when taking supplements.

3. Magnesium deficiency

This is the most overlooked reason. Magnesium is required as a cofactor for the enzymes that convert vitamin D into its active form. It is estimated that 50 to 60% of the European population has insufficient magnesium. Without enough magnesium, D3 from a supplement cannot be activated — regardless of the dose.

4. Absence of vitamin K2

Vitamin D strongly increases calcium absorption from the gut. Without K2 to direct that calcium toward bones and teeth, it can accumulate in arterial walls. Studies link long-term high-dose vitamin D without K2 to increased calcium deposits in the arteries.

The magnesium connection you are likely missing

Magnesium is a cofactor in at least two enzymatic steps in the activation of vitamin D. Without sufficient magnesium, vitamin D from a supplement cannot be converted into its active hormonal form. The point: addressing a magnesium deficiency first can significantly improve your vitamin D status, without increasing your vitamin D dose.

A 2018 study in The American Journal of Clinical Nutrition found that magnesium intake clearly influenced the relationship between vitamin D supplementation and vitamin D status — indicating that sufficient magnesium is a prerequisite for effective supplementation.

Why D and K2 always belong together

Vitamin K2 (MK-7) activates two important proteins:

Osteocalcin incorporates calcium into the bone matrix. Without K2 activation, calcium cannot be effectively bound to bone.
Matrix Gla protein (MGP) prevents calcium from precipitating in arterial walls. It is only active in its K2-dependent form.

Vitamin D without K2 is calcium transport without a traffic controller. In clinical research, the combination of D3 and K2 improves bone mineral density more effectively than either one alone.

Signs of a vitamin D deficiency

Fatigue and low energy vitamin D receptors are also located in mitochondria
Low mood, especially in winter vitamin D plays a role in serotonin production
Frequent infections vitamin D is important for the innate immune system
Bone and muscle pain classic signs of a severe deficiency
Hair loss vitamin D receptors in hair follicles regulate the growth cycle

The PPH standard

PPH Liposomal Vitamin K2 + D3 combines 45 mcg of vitamin K2 (MK-7) with 25 mcg (1,000 IU) of vitamin D3 in our dry-liposomal form. This form overcomes the absorption threshold of fat-soluble vitamins by encapsulating both in a phospholipid bilayer.

Vitamin K2 (MK-7) 45 mcg (60% EU-RI)
Vitamin D3 25 mcg / 1,000 IU (500% EU-RI)
Liposomal delivery overcomes the absorption threshold of fat-soluble substances
MK-7 as the K2 form the longest duration of action and the best evidence base

Conclusion and next step

You cannot solve a vitamin D deficiency simply by taking a pill. It requires attention to absorption, to the cofactors that enable conversion, and to the co-nutrient that directs calcium in the right direction. If you skip any of these steps, you can take supplements for years with little result.

Because your vitality is not optional — it is essential.

Frequently asked questions

For adults, 1,000 to 2,000 IU per day is usually recommended. In the case of a confirmed deficiency, a doctor may temporarily recommend a higher dosage. Have your levels re-measured after 3 months.

D3 (cholecalciferol) increases blood levels of 25-OH-vitamin D about twice as effectively as D2 at the same dosage. PPH uses only D3.

Preferably, yes. A blood test for 25-OH-vitamin D provides a clear picture. Values of 75 to 150 nmol/L are considered optimal; below 50 nmol/L is considered a deficiency. Measuring before and after a supplementation period confirms both the necessity and the effect.

Sources

Dai, Q. et al. (2018). Magnesium status and supplementation influence vitamin D status. American Journal of Clinical Nutrition. pubmed.ncbi.nlm.nih.gov/30541089/
Maresz, K. (2015). Proper Calcium Use: Vitamin K2 as a Promoter of Bone and Cardiovascular Health. Integrative Medicine. www.ncbi.nlm.nih.gov/pmc/articles/PMC4566462/
Holick, M.F. (2007). Vitamin D Deficiency. New England Journal of Medicine. pubmed.ncbi.nlm.nih.gov/17634462/
European Commission (2022). Vitamin D and sunlight exposure. ec.europa.eu/