Vitamin D

Listen—how is it that every year we service our car: we change the oil, filters, wiper blades, and who knows what else… but we don’t even know something as basic as our vitamin D level? And sometimes—even when we do know it’s very low—we still don’t take it seriously. Even my doctor friends don’t.

Yet if a car’s engine oil drops below the minimum mark, we immediately think: hmm, the consequences could be pretty expensive.

Just like we have the CSDD vehicle inspection guys who point out a fault that needs fixing at the mechanic, we also have doctors who often point out a deficiency in a vitamin, a micro- or macroelement that we “should fix urgently”—if we actually want that vehicle to run.

Vitamin D is not just a “regular vitamin.” It’s also a powerful steroid hormone that interacts directly with our DNA. Like a conductor of DNA, it activates or suppresses more than 5% of the entire protein-coding human genome. (1)

If that still didn’t convince you, here are the key functions of vitamin D:

Bone health — Vitamin D supports calcium absorption in the gastrointestinal tract, which is essential for strong bones and teeth. Think of it as “reverse engineering”: if you’ve had vitamin D deficiency for years, over time you’ll end up with poorer bone and dental health.

Immune regulation — Vitamin D supports our immune system by regulating the production of various antimicrobial peptides—part of the body’s natural defense mechanisms against pathogens in our environment (viruses, bacteria). “Reverse engineering” here means more frequent illness in the presence of deficiency.

Muscle health — Adequate vitamin D levels are important for optimal muscle function—especially later in life, when the risk of falls increases. Reverse engineering: years of deficiency = weaker muscles and bones = higher risk of serious injury = a shorter lifespan.

Cell division and differentiation — Vitamin D plays a role in processes such as cell growth, differentiation, modulation, division, and apoptosis (programmed cell death). Proper function of these processes is vital for preventing and eliminating cancer cells. Reverse engineering: long-term deficiency = higher cancer risk.

Inflammation reduction and neuromodulation — Vitamin D has anti-inflammatory properties and contributes to maintaining optimal brain function. Reverse engineering: years of deficiency = higher risk of dementia later in life. (2,3)

Cardiovascular health — Studies describe vitamin D’s positive impact on cardiovascular health. Reverse engineering: long-term deficiency = higher risk to heart health. (4)

Hope I’ve convinced you by now!

In other words: vitamin D is essential if many of our body’s functions are to work optimally.

And yet, as a society, we treat the importance of this vitamin-hormone carelessly. One large U.S. study reports that around 70% of the U.S. population has vitamin D levels below 30 ng/ml—below the lower end of the reference range. (5)

If we don’t get enough UVB exposure in daily life (direct sunlight), the natural synthesis of vitamin D in the skin isn’t triggered. That’s where the well-known alternative comes in: vitamin D supplementation.

Remember: it’s very important to know an appropriate vitamin D dose and the safest upper limit for adults—4,000 IU. This dose can help those with deficiency (20 ng/ml and below) reach a normal vitamin D level. Supplementing with 1,000 IU typically raises vitamin D by about 5–10 ng/ml on average.Important: children’s doses depend on age group—before starting, consult your doctor!

Regularly checking vitamin D levels in blood tests is very important, because it allows you to monitor individual differences in absorption speed depending on the dose—especially if you’re taking very high doses.

I’d be cautious with very high vitamin D doses if you’re not planning to test your levels soon. Vitamin D is fat-soluble, and toxicity is a real thing.

With excessive vitamin D intake, calcium absorption increases—and like all minerals in our body, calcium needs to be in an optimal range for organs to function properly. Too much or too little, and things start to go wrong. Early symptoms may include nausea, vomiting, and weakness, which can progress to serious kidney damage, heart rhythm disturbances, confusion, and disorientation.

As my therapist tells me—and I’ll tell you too: dear ones, get your regular technical inspection done.

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References

1. Carlberg et al., Vitamin D and Its Target Genes, Nutrients 2022, https://doi.org/10.3390/nu14071354

2. Miller et al., Vitamin D supplementation appears to increase plasma aβ40 in vitamin d insufficient older adults: a pilot randomized controlled trial, J Alzheimers Dis. 2016, 52:843-7. 10.3233/JAD-150901

3. Annweiler et al., Vitamin D in dementia prevention. Ann NY Acad Sci. 2016, 1367:57-63. 10.1111/nyas.13058

4. De la Guia-Galipienso et al., Vitamin D and cardiovascular health. Clinical Nutrition 2021, https://doi.org/10.1016/j.clnu.2020.12.025

5. Cui A et al., Prevalence, trend, and predictor analyzes of vitamin D deficiency in the US population, 2001-2018. Frontiers in Nutrition, https://doi.org/10.3389/fnut.2022.96537