Vitamin D Day

What we know about vitamin D's discovery

Vitamin D wasn't discovered on one specific day. Research spanned decades in the early 20th century. Edward Mellanby found something in cod liver oil that prevented rickets in dogs in 1919. Elmer McCollum and Marguerite Davis discovered vitamin D in rats in 1922. Harry Steenbock figured out how to fortify milk with it the same year.

The discovery is credited to multiple scientists. Their work formed the foundation of what we understand today.

There are two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

The global deficiency numbers are staggering

1 billion people worldwide have vitamin D deficiency. Another 50% of the global population has vitamin D insufficiency.

Approximately 1 billion. That's not a typo.

In the United States alone, about 35% of adults are vitamin D deficient. About 50-60% of nursing home residents and hospitalized patients lack adequate levels.

The prevalence varies by region. The Eastern Mediterranean region and lower-middle-income countries show the highest rates. People at high latitudes face greater risk. Winter-spring deficiency rates are 1.7 times higher than summer-autumn.

Globally, 47.9% of people have serum levels below 50 nmol/L. That's clinical deficiency territory.

The aging breakthrough that happened in 2025

In May 2025, major news. Researchers at Harvard and Mass General Brigham published findings from the VITAL trial. Nearly 26,000 participants tracked for five years.

The result: Vitamin D supplementation slows biological aging.

Specifically, 2,000 IU of vitamin D3 daily preserved telomeres. These are the protective caps on the ends of chromosomes. They shorten as we age. They're linked to disease development.

The vitamin D group lost 140 fewer base pairs of DNA over four years compared to placebo. Based on previous studies, that could equal up to three years of aging.

"This is the first large-scale and long-term randomized trial to show that vitamin D supplements protect telomeres," said Dr. JoAnn Manson, principal investigator.

The same study had already shown vitamin D reduces inflammation and lowers risks of advanced cancer and autoimmune diseases.

Other major developments from this year

Multiple Sclerosis: High-dose vitamin D (100,000 IU every two weeks) reduced MS disease activity. Each 100 nanomole-per-liter increase in vitamin D was linked to a 42% reduction in disease activity risk over two years.

Cardiovascular Risk: A study on American Indian adolescents found vitamin D deficiency independently associated with metabolic syndrome. Thirteen years after baseline, diabetes incidence rates were significantly higher among those with vitamin D deficiency.

Market Growth: The vitamin D supplement market exceeded $1.1 billion in 2020. Projected to reach $1.6 billion by 2025.

Why this day falls on November 2

November marks when vitamin D levels start dropping in the northern hemisphere. The sun angle changes. Days get shorter. People spend more time indoors.

All these factors increase the risk of deficiency. November is exactly the right time for awareness.

The people most at risk of deficiency

The Robert Koch Institute identifies high-risk groups:

• People who rarely go outside (chronically ill, care-dependent, immobile)
• Older people (production decreases with age)
• Infants (shouldn't have direct sun exposure)
• People with dark skin (higher pigmentation reduces UV transmission)
• Those with kidney disease, liver disease, chronic gastrointestinal diseases
• Patients on drugs that inhibit vitamin D metabolism (anti-epileptic drugs, cytostatics)

Why vitamin D deficiency often goes undetected

Vitamin D levels aren't routinely checked in standard health screenings.

Symptoms are vague. Muscle pain. Hair loss. Susceptibility to infections. These could indicate many things.

Deficiency develops gradually. It's hard to pinpoint.

Many people still don't know Vitamin D Day exists or why vitamin D matters.

What vitamin D actually does in your body

It's not just about bones anymore. Vitamin D is now recognized as a "multifunctional vitamin."

It promotes calcium and phosphate absorption from the intestine. It helps incorporate these into bones, supporting mineralization.

It contributes to the immune system. The psyche. Muscle function.

It regulates genes. Using receptors, it influences protein formation, messenger substances, and enzymes.

Severe deficiency (below 30 nmol/L) dramatically increases the risk of excess mortality, infections, and many diseases.

The reality about getting vitamin D from food

You can only get around 10% of needed vitamin D from food. Even vitamin D-rich foods.

Fatty fish. Milk. Eggs. Butter. Mushrooms. Avocado. They all provide some. But it's not enough.

Fortified foods help. Fortified milk and spreadable fats can fill gaps. But they're still supplementary.

The body's own synthesis through sun exposure is the primary source. That's the problem when you're indoors or at high latitudes.

What actually works to boost your levels

Check your levels: A blood test shows your 25-hydroxyvitamin D concentration. Experts disagree on ideal levels. The Institute of Medicine recommends 20 ng/ml. The US Society of Endocrinologists suggests 30 ng/ml.

Get sun exposure: About 30 minutes in summer (morning or late afternoon). One hour in spring and fall. Face, arms, and hands minimum. Balance between production and sunburn risk.

Consider supplements: 2,000 IU daily has proven effective in large-scale trials. Free from unnecessary additives is best. Combined with MCT oil works well since vitamin D is fat-soluble.

Food fortification: Some countries have implemented systematic vitamin D food fortification. It works. Ireland saw deficiency drop from 55% to 14% in elite athletes through supplementation programs.

The connection to Blue Zones around the world

Dan Buettner identified five Blue Zones worldwide. Places where people regularly live past 100.

Ikaria, Greece. Okinawa, Japan. Ogliastra, Sardinia. Loma Linda, California. Nicoya, Costa Rica.

All are in subtropical to tropical regions. Residents get plenty of sunshine. Good basic requirement for vitamin D production.

Unprocessed food. Exercise. Strong social cohesion. And sun. The combination works.

The potential for preventing cancer deaths

Scientists at the German Cancer Research Center found that fortifying food with vitamin D could prevent over 100,000 cancer-related deaths in Europe each year.

100,000 deaths. From food fortification.

Why vitamin D deficiency matters so much

Nearly 50% of the global population deals with vitamin D deficiency. It affects bone health, immune function, mental health, muscle strength, and now we know it affects biological aging.

The solution exists. Sun exposure. Supplementation. Food fortification.

But implementation remains inconsistent worldwide.

What Vitamin D Day is actually trying to do

The recurring event is popular in the USA. Organizations like GrassrootsHealth highlight it. In Germany, the German Food Association works to raise awareness.

The goals are simple:

• Draw attention to vitamin D's health importance
• Encourage people to check their vitamin D supply
• Make people aware of deficiency consequences
• Highlight ways to increase intake during months with less sunshine

The message we need to hear in 2025

Vitamin D deficiency affects approximately 1 billion people worldwide. The consequences are measurable. The solutions are available.

Recent research shows vitamin D supplementation can slow biological aging by preserving telomeres. It can reduce disease activity in multiple sclerosis. It can lower cardiovascular risk factors.

But only if people know about it. Only if they check their levels. Only if they take action.

That's why November 2 matters. That's why Vitamin D Day exists.