After nearly 30 years in practice, I have come to a simple conclusion: the vitamin D story does not make sense.
When I first began practicing, very few people were taking vitamin D supplements. The primary source was cod liver oil, which naturally provided vitamin D alongside vitamin A in balanced proportions, without toxicity or side effects.
According to NHANES III (1988–1994), approximately 45% of Americans had vitamin D levels of 30 ng/mL (75 nmol/L) or higher. By NHANES 2001–2004, that number had dropped to about 23%.
In the 1980s and early 1990s, high-dose vitamin D supplementation was uncommon. Testing was rare, and many foods that are fortified today either were not fortified or contained much lower amounts.
Today, vitamin D is everywhere. It is added to foods, included in multivitamins, and widely sold as a standalone supplement. Millions of people take it daily. Both conventional and holistic practitioners routinely recommend it, and blood levels are checked far more frequently than in the past.
Yet despite this, concern about vitamin D deficiency is more widespread than ever.
There is a valid reason for that concern. Low vitamin D levels are consistently associated with weakened immune function, certain cancers, autoimmune conditions, and other health issues.
But from a practical standpoint, this raises an important question:
If people are consuming significantly more vitamin D today than they did 40 years ago, why does deficiency remain so common?
In my view, based on decades of clinical observation, the focus has shifted too heavily toward vitamin D intake rather than vitamin D metabolism.
Vitamin D is not biologically active when ingested. It must first be converted in the liver to 25-hydroxyvitamin D, then activated in the kidneys into its usable form. If either organ is not functioning optimally, vitamin D metabolism may be impaired, regardless of intake.
Vitamin D deficiency is often less about intake alone and more about broader metabolic processes.
Many practitioners emphasize achieving a target lab value while overlooking the systems responsible for processing vitamin D.
The body also depends on key cofactors to properly utilize vitamin D. Magnesium plays a central role in its metabolism, and calcium works closely with it. In clinical practice, imbalances involving magnesium, calcium, iodine, vitamin C, and trace minerals often accompany poor nutrient utilization and broader metabolic dysfunction.
The body is not a chemistry set where one isolated nutrient determines health. It is an interconnected system.
I will also offer a cautious observation: many practitioners who prescribe vitamin D may not fully consider how it is manufactured or the broader implications of its production. Vitamin D supplements are not simple, natural substances; they are highly processed products typically derived from lanolin, a wool-based material that must be chemically extracted, purified, and converted into vitamin D3.
The concern is not merely that the source is animal-based. It is that the final product results from an industrial process that can involve solvents, multiple purification steps, and potential contaminants if sourcing and testing are not rigorous (entirely manufactured in India and China). In that sense, many vitamin D supplements are manufactured products rather than whole-food nutrients. I consider it a drug.
A more accurate way to frame the issue is this: the problem is not vitamin D itself, but the assumption that a concentrated, isolated, and heavily processed form is automatically benign simply because it is widely recommended. At higher doses, or with poor-quality manufacturing, these products may contribute to toxicity concerns, especially when they elevate calcium levels without consideration of broader mineral balance and organ function.
Over time, research may show that long-term use of high-dose synthetic vitamin D is less benign than currently assumed. We already know that excessive intake can contribute to elevated calcium levels, kidney stones, kidney stress, and soft tissue calcification in susceptible individuals.
History has repeatedly shown that prolonged use of isolated nutrients in concentrated forms can lead to unintended consequences.
But the larger issue is not toxicity. The larger issue is that we may be treating a symptom rather than addressing the cause. Low vitamin D levels may reflect impaired liver or kidney function, chronic inflammation, obesity, insufficient sunlight exposure, metabolic dysfunction, mineral imbalances, or other underlying issues that supplementation alone cannot correct.
For decades, the question has been:
“How much vitamin D should we take?”
Perhaps the better question is:
“Why are so many people unable to properly metabolize and utilize vitamin D in the first place?”
Until we address that, we risk chasing lab values while overlooking the dysfunction that created them.
Footnotes
- Vitamin D supplementation and testing have increased substantially in the United States since the 1980s.
- Vitamin D is converted in the liver to 25-hydroxyvitamin D and then activated in the kidneys.
- Magnesium is a required cofactor in vitamin D metabolism.
- Obesity, inflammation, liver and kidney function, aging, and sunlight exposure all influence vitamin D status.
- Excessive supplementation can lead to hypercalcemia, kidney stress, kidney stones, and soft tissue calcification.
Mark Colafranceschi, D.C. • Licensed Chiropractic Physician – Arizona License #009154 • Scottsdale, Arizona