Is vitamin D the unsung hero of human health?

Vitamin D deficiency is a global crisis, Jennifer Aliano from GrassrootsHealth, tells Natalie Li, but it’s time to take this vital nutrient far more seriously.

Summertime offers a natural opportunity to boost vitamin D levels through sun exposure. Yet balancing sun safety and optimal health can be a challenge, especially in in the UK, where sunlight is limited for much of the year.   

Vitamin D has long been associated with bone health, but its significance runs far deeper. It plays a vital role in immune function, cardiovascular health, pregnancy outcomes, and even cancer prevention.   

Vitamin D can be obtained from sunlight exposure, certain foods, and supplements. Oily fish like salmon, mackerel, and sardines are excellent food sources, as are egg yolks, beef liver, and fortified foods like cereals and milk alternatives. However, it can be difficult to achieve sufficient vitamin D levels from sunshine and food alone, making supplements necessary for most individuals.  

UK government advises that everyone should consider taking a daily vitamin D supplement during the autumn and winter.   
  
The UK recommended daily vitamin D intake for anyone over the age of one is 10 micrograms (ug) or 400 international units (IU). According to vitamin D scientists and experts, this recommendation is far too low. They suggest a personalised vitamin D intake necessary for supporting optimal vitamin D levels of 40-60 ng/ml (100-150 nmol/L), which requires an intake closer to 4000-8000 IU of vitamin D per day. Achieving this through sunshine and food alone can be a challenge; especially in individuals whose skin has been slathered with high factor sunscreen.  

Taking it personally: testing and tailoring

Despite its nickname — the “sunshine vitamin,” — many people struggle to get enough vitamin D from sunlight alone. Vitamin D deficiency remains the most common nutrient deficiency worldwide.  

Getting enough vitamin D often requires more than diet or sun alone, especially in higher latitudes. The only way to determine sufficiency is through blood testing, measuring serum levels of 25-OHD. “The only way to tell if you’re getting enough is to measure your 25-OHD level,” says Jennifer Aliano, executive director at GrassrootsHealth, a non-profit health initiative focused on vitamin D awareness.  

Research has shown that vitamin D impacts nearly every cell in the body. “That is a non-hormonal action of vitamin D, nothing to do with parathyroid hormone, a chemical messenger made by your parathyroid glands located behind your thyroid in the neck, or bone health,” Aliano explains. “It’s utilised right there in the cell.”  

Aliano has spent over a decade researching the impact of vitamin D and advocating for greater awareness. “Almost 90% of US adults are below 40 nanograms per millilitre,” she explains. “If you’re not supplementing, you’re very, very highly likely to be deficient or insufficient.”  

GrassrootsHealth was founded in 2007 by Carole Baggerly after her own battle with breast cancer and osteoporosis. Through research, she discovered a striking connection between vitamin D and both conditions. “Carole started GrassrootsHealth to be the voice of the vitamin D researchers,” says Aliano. Since then, the organisation has conducted an international study with over 20,000 participants, tracking the effects of vitamin D supplementation.  
  
“We are meant to make vitamin D,” Aliano says, “but the darker your skin colour, the longer you need to be in the sun to make the same amount as someone with lighter skin.”   

Seasonal changes, geographical location, and lifestyle factors all contribute to widespread deficiency.  

Food sources of vitamin D are limited. “It is incredibly difficult to get enough from food,” she notes, making supplementation often necessary. However, the right dosage varies from person to person. “There’s no single dose for everybody,” she adds. “Everyone needs an individualised or personalised dose so it’s important to work with a nutritional therapist or healthcare professional.”  

It is incredibly difficult to get enough (Vitamin D) from food

Supplementation should be taken with a fatty meal for optimal absorption. “Just take it when you know you’re going to remember,” Aliano recommends. A dose of 10,000 IU (0.25mg) per day may sound high, but she reassures, “your skin can make up to 25,000 (0.625mg) IU in one sun session.” Higher doses, above 8,000 IU, may also benefit from vitamin K2, which helps regulate calcium absorption and prevents arterial calcification, otherwise known as the ‘hardening of the arteries’ when calcium forms hard crystals in the blood vessel wall.   

Vitamin K2 plays an essential role in regulating calcium. “Vitamin D pulls the calcium in, K2 shuttles it to where it needs to go,” Aliano explains. Without it, calcium may end up deposited in arteries. Fermented foods like natto, kimchi, and aged cheeses are rich in K2 and provide a synergistic benefit to vitamin D supplementation.  

Womb for improvement 

Few people realise the critical role vitamin D plays in pregnancy. “The role of vitamin D starts at conception, preconception even,” says Aliano. “The health of your pregnancy really does affect the lifelong health of that child.”  

During pregnancy, a woman’s body undergoes a unique transformation in how it processes vitamin D. “By week 12, the level of 1,25-OHD in her blood would be toxic and potentially fatal to a non-pregnant individual,” she explains. However, for pregnancy to proceed smoothly, optimal vitamin D levels, at least 40 nanograms per millilitre or 100 nanomoles (nmol) per litre, are essential. Deficiency during pregnancy has been linked to increased risks of preterm birth, preeclampsia, gestational diabetes, and even autoimmune diseases later in life.  

Traditional societies, Aliano notes, had naturally higher vitamin D levels. “Pregnant women in tribal populations had much higher vitamin D levels than all the other groups that were studied,” she says, reinforcing the evolutionary need for adequate exposure to sunlight and supplementation.  

Vitamin D in hospitals 

A striking example of vitamin D’s potential comes from a North Dakota hospital project, where patients’ vitamin D levels were measured upon admission. “The vast majority were well below 20ng/ml” Aliano reveals. Using GrassrootsHealth’s calculator, doctors prescribed loading doses of 25,000 IU daily, followed by maintenance doses.  

The results were remarkable. “They saw reduced infection rates, reduced levels of CAUTI (Catheter-associated Urinary Tract Infection) and CLABSI (Central Line-Associated Bloodstream Infection), and even received recognition from the state health department,” she says. Brain injury patients admitted to the hospital in comas began waking up and communicating with full and quicker recoveries, a testament to vitamin D’s potential in recovery and rehabilitation.  

Toxicity and research flaws 

One persistent concern is toxicity. Aliano dismisses the fear, explaining, “It is incredibly difficult to take too much vitamin D.” Toxicity is typically only seen at levels above 150-200 nanograms per millilitre and involves hypercalcemia, a condition in which the calcium level in the blood becomes too high.  “Most cases of toxicity come from manufacturing errors or extreme doses like 100,000 IU per day,” she clarifies.   

And while toxicity is rare, there is still no reason to take too much vitamin D 

“The goal should always be to take just the right amount to achieve and maintain a vitamin D blood level of 40-60 ng/ml or up to 80-100 ng/ml for certain conditions,” explains Aliano.  

“While there are therapeutic uses of vitamin D, where levels above 100 ng/ml are necessary and helpful, in these circumstances it is important to work with a knowledgeable vitamin D practitioner who can help guide supplementation and monitor for potential toxicity. 

Vitamin D research also faces challenges. Studies like the VITAL trial failed to measure achieved blood levels in most individuals, limiting their conclusions. “They only gave 2,000 IU a day, which is not enough for most people to reach the optimal range,” says Aliano. Additionally, the placebo group was allowed to take up to 800 IU a day, skewing comparisons between the group. True vitamin D research, she argues, should focus on dosing participants to a set serum level and observing health outcomes, such as GrassrootsHealth’s preterm birth study, which found a 60% reduction in risk among women with vitamin D levels of 40 nanograms per millilitre or higher in comparison to women with vitamin D levels below 20.  

Aliano remains committed to carrying forward Carole Baggerly’s vision, ensuring that vitamin D’s role in health does not go unnoticed. “When you leave vitamin D out, you’re leaving a huge piece of the puzzle out,” she says.   

Whether addressing pregnancy health, chronic disease, or hospital outcomes, the evidence is clear, vitamin D is far more than just a bone health nutrient.