Prior to COVID-19, if someone asked you whether they needed a vitamin D supplement, you’d probably have told them not to worry about it – or recommended a multivitamin with a few hundred IUs of D. And people who lived in warm climates would have thought that just getting some sun was enough. Well, the latest research says we were all wrong.
According to recent research into worldwide vitamin D levels by Cui et.al (2023) (1), 15.7% of the global population is deficient. That’s over one billion people!
Why the recommended daily allowance for vitamin D needs to be revised
But that’s just the beginning. It seems that the recommended daily allowances (RDAs) for vitamin D, which range from 600 to 800 IU per day, are also inadequate. Researchers are calling for significant increases to both daily recommendations and therapeutic doses.
That’s because the sunshine vitamin is more important than many of us realize. Low levels of D have been shown to increase the risk for numerous conditions, including Alzheimer’s, Parkinson’s, osteoporosis, irritable bowel disease, asthma, rheumatoid arthritis, psoriasis, many cancers (including colon, breast, ovarian, and prostate), cardiovascular disease, infections like COVID-19, and even some mood disorders.
Vitamin D is essential for so many functions that keep us healthy. So why are RDAs lower than many researchers feel they ought to be? Should those at risk for deficiency be supplemented at much higher doses? Is it safe to increase the limits?
Current RDAs
McCullough et al. (2019) provide a fascinating summary of the history of vitamin D. (2) During the 1930s and 40s, physicians used vitamin D to treat conditions such as psoriasis, asthma, rheumatoid arthritis, and tuberculosis – and often at substantially higher doses than used today.
Unfortunately, there were some reports of vitamin D-induced hypercalcemia, usually after a prolonged daily intake of these megadoses. Instead of experimenting with reduced amounts, doctors decided that D was toxic and stopped using it to treat diseases.
At the same time, the RDA was reduced to the amount present in a single teaspoon of cod liver oil, which is approximately 400 IU. The RDA remains in place even today.
The role of this vitamin cannot be underestimated
In the late sixties, researchers discovered that vitamin D3 had a crucial role to play within cells, and the link between vitamin D deficiency and the risk of certain diseases became apparent. These included Alzheimer’s, asthma, autoimmune conditions, multiple sclerosis, psoriasis, rheumatoid arthritis, many cancers (including breast, colon, prostate, and skin), depression, diabetes, fibromyalgia, falls, fractures, osteoporosis, Parkinson’s, and more.
So the questions once again arose: How much vitamin D do we need for good health? How much is safe for daily and therapeutic use?
10,000 IU/day was suggested as a safe limit back in 2007. In their seven-year study, McCullough et al. (2019) found that a daily oral dose of 5,000 IUs was well tolerated and safe. In some patients, they increased the dose to 60,000 IUs with no adverse effects. (2)
The Complexity of Vitamin D
Numerous complex processes must take place for vitamin D to turn into an active form that the body can use. It starts with the skin being exposed to the sun’s UV rays. (For simplicity, we’ll discuss getting it from the sun rather than food, which contains very little D.)
Exposure to UV rays triggers the production of a certain type of cholesterol within the skin; this cholesterol is then converted into an inactive form of D3, which ends up in the liver. With the help of an enzyme, this inactive form of D3 is further converted to calcifediol – also known as calcidiol or 25-hydroxyvitamin D3, abbreviated 25(OH)D3. It then leaves the liver and is bound in the blood by a vitamin D-binding protein. This form, which is still inactive, is the one that blood tests measure to estimate vitamin D levels in the body.
Calcifediol is further activated by an enzyme (CYP27B) found primarily in the kidneys. This enzyme also requires activation before it can do its job. In a complex process, low calcium and phosphorus levels in the blood stimulate the parathyroid gland to produce parathyroid hormone (PTH). PTH then activates the enzyme, resulting in the conversion of calcifediol to calcitriol, the active form of vitamin D.
What impacts our ability to produce more or less vitamin D?
It is this process that controls the balance of calcium in the body, which is why vitamin D affects bone health. It also regulates hundreds of genes and maintains our immune systems (hence the connection to COVID-19) (3). According to SJ Wimalawansa of the CardioMetabolic and Endocrine Institute, 75% of our immune system depends on vitamin D to function! (4)
And of course, we know that our bodies produce more or less vitamin D depending on the season, time of day, our distance from the equator, and sunscreens. Production is also impacted by age, weight, diet (especially vegans and vegetarians), chronic health issues, and pollution levels.
That’s a lot of variables.
So how much do we really need?
For most of us, simply being in the sun will not give us enough vitamin D.
Wimalawansa recommends daily exposure of between 45 to 60 minutes with at least a third of the body exposed to direct summer-like sunlight between 10.30 am and 1.30 pm. This would generate in the region of 2,000 to 10,000 IUs (4). No wonder vitamin D levels across the globe are so low!
That’s where supplements – and blood tests – come in.
The Difficulty of Measuring vitamin D
A vitamin D test measures 25(OH)D from D3 (calcifediol derived from the sun and animal products) and D2 (calcidiol from plant-based sources such as sun-exposed mushrooms). Depending on the country, results are reported in ng/mL (nanograms per milliliter) or nmol/L (nanomoles per liter).
But 25(OH)D is an inactive form. And because the conversion happens in many places, including within some cells, and depends on many factors (including low levels of calcium and phosphorous), it’s hard to predict how much active D will be in the bloodstream after the final conversion.
Researchers are, however, gaining a better understanding of these processes and factors, which is why they now believe the requirements are much higher than we once thought.
By current standards, a blood level below 20 ng/mL or 50 nmol/L is a sign of deficiency. There is, however, a growing call to increase this level to 30 ng/mL (or 75 nmol/L). Some researchers are even arguing that a minimum of 40 ng/mL (100 nmol/L) is needed to reduce the risk of some cancers, cardiovascular disease, infectious diseases, diabetes, and COVID-19. That’s twice the current standard.
This is what you need to know
RDA levels are currently between 400 AND 800 IUs. There’s also a call for these to be increased in adults (18 to 75) to between 1,000 and 2,000 IUs per day with an upper tolerable dose of 4,000 per day. For adults older than 75, the suggestion is between 2,000 and 4000 IUs per day, with the same upper tolerable dose of 4,000 IUs.
When there’s a deficiency, therapeutic doses may be required. Some experts say that adults can take as much as 6,000 IUs per day for up to three months – and those who are particularly obese, or weigh more than 90 kg, can go as high as 10,000 IUs per day (5).
Higher doses should be supervised by a medical practitioner, who would monitor the patient for hypercalcemia.
The Bottom Line
Vitamin D is essential for life, and we were designed to get it from the sun. Since we live so differently than our ancestors, it makes sense that we might need to boost this powerful nutrient to keep our bodies at their best.
And whilst the researchers continue to thrash out how much D we need, it’s up to us to figure out how much to take to optimize our health.
