Vitamin D is an essential fat-soluble vitamin. It’s sometimes called the “sunshine vitamin” because your skin makes it when exposed to the sun.
It’s also the most common nutrient deficiency!
Like most vitamins, vitamin D has many functions in the body. It’s mostly known for its ability to help build strong bones. But, vitamin D is also important for a healthy immune system, digestive system, heart and mental health, blood sugar regulation, fertility, and resistance to cancer.
FUN FACT: Vitamin D is the vitamin with more scientific articles published since 2000 than any other vitamin.
Let’s talk about the many roles vitamin D has in promoting good health. I’ll also go over the different forms of vitamin D and spell out what exactly constitutes a deficiency. Finally, I’ll give you three sources of this critical nutrient and suggest much you should get.
Make sure you’re getting enough!
Vitamin D in the body
Vitamin D (cholecalciferol) is the form of vitamin D that is produced in your skin by the sun (but only under ideal conditions), it’s what’s in your vitamin D supplement and what’s found in foods like fluid milk, fatty fish, butter and eggs.
Cholecalciferol isn’t “active” in your body. To do its wonders, it first needs to be converted into the active form.
This is a two-step process. Firstly, the liver converts it into 25(OH)D (calcidiol); this is what’s measured in your blood when you get a vitamin D test.
Then secondly, 25(OH)D (calcidiol) is converted by your kidneys into 1,25(OH)D (calcitriol). It’s this third form, calcitriol, that circulates in your blood and enables your intestines to absorb calcium.
Vitamin D acts like a hormone! That means it’s produced in one part of the body (e.g. the skin/kidneys), and travels through the body (blood) to act on another part of the body (cells or tissue) and stimulate it into action (e.g. the intestines absorbing calcium).
Vitamin D, 25(OH)D (calcidiol) also travels to nearly every other cell type in your body: immune, brain, muscle, pancreatic, etc where it is take up and also converted into the active form. Once inside the cell, it interacts with your DNA and modifies your genes. This is why it seems too good to be true, that vitamin D can have an impact on so many different bodily functions.
Vitamin D is “fat soluble” which technically means it is found in both the watery parts, like blood, and it can be absorbed into fat cells/tissue and your liver.
This means that you are able to store vitamin D, unlike vitamin C or B vitamins. for future use. But, the storage capacity isn’t that huge. Vitamin D stores can be depleted within a few months which is why vitamin D deficiency is common despite your body’s ability to store it.
FUN FACT: Fish liver oil supplements contain vitamin D, but not fish oil supplements – it’s the liver that stores vitamin D.
Vitamin D for bones
Vitamin D is most known for its importance for bone health. Bones are alive and are constantly remodeling themselves. This means they, as with all tissues, need a constant supply of nutrients for repair and maintenance. It IS possible to starve your bones; osteomalacia, osteoporosis, and frailty, anyone?
How does vitamin D help your bones?
Vitamin D helps your body (small intestines) absorb calcium more efficiently. And the mineral calcium is one of the major players needed to “mineralize” and strengthen our bones. Not to be outdone though, the minerals magnesium and phosphorus are also essential.
FUN FACT: New research shows it’s not just the kidneys that activate 25(OH)D into 1,25(OH)D – bone cells can do this too!
Vitamin D works with other hormones (PTH) to ensure optimal levels of calcium in the blood. When it comes to calcium, the body always prioritizes the blood over the bones. This is because the blood transports calcium around the body for critical functions like keeping your heart beating or being able to move your muscles. This is why it’s more important for your body to maintain the blood calcium levels versus sending calcium to your bones.
We all lose some calcium every day as part of bone turnover. We need to replace the calcium that’s lost and we get that from our diet. When we get enough dietary calcium, any excess is stored in your bones. This is how your bones are mineralized and strengthened.
When there isn’t enough calcium in the blood two things happen to raise this level. Firstly, vitamin D stored in the liver is activated and mobilized. It then travels to the kidneys where it’s turned into the hormone that enables your intestines to absorb more calcium from food. Secondly, the body also removes some calcium stored in your bones to raise levels in the blood.
When you don’t get enough vitamin D (and calcium) regularly, you can’t absorb enough calcium from food so your body will steal more from your bones. Over time, your bones can become weak and brittle. In children, severe vitamin D deficiency can cause rickets, and in adults, it can cause osteomalacia. With less severe vitamin D (and/or calcium) “insufficiency” (as opposed to a more severe “deficiency”), osteoporosis can develop over the long term.
Having enough 25(OH)D in the blood is associated with higher bone density. Studies show that supplementing with vitamin D may reduce the risk of falls and bone fractures.
FUN FACT: The strongest evidence for what vitamin D deficiency actually causes is rickets and osteomalacia. Other diseases and conditions do have evidence, but it’s not clear to what extent they’re caused by vitamin D deficiency/insufficiency (functional deficiency). It’s also not clear to what extent other factors also come into play via synergy (magnesium, vitamin K2, boron, zinc, vitamin C etc).
Vitamin D, the immune system, and inflammation
Vitamin D is a key player in immunity. Cells of the immune system have vitamin D receptors which eagerly wait for vitamin D to bind to them. These immune cells then convert vitamin D into its active form; a hormone that regulates the activity (genes) of the immune cells.
Vitamin D modulates both the innate and adaptive immune response. All that needs to be understood is that vitamin D supports the immune system’s dual strategy in fighting infections. It’s the first line of defense by fighting new infections that it sees as a general threat – H1N1 virus (innate). Then, being able to store information on that threat, just in case it comes back (adaptive). The next time H1N1 comes around, you might only get a brief “cold”.
Vitamin D is well understood for its role in viral and bacterial infections.
Several studies have also shown a link between low levels of vitamin D and the risk for immune-related conditions like atopic dermatitis, allergies, asthma, Type 1 diabetes, rheumatoid arthritis, and more.
Vitamin D has anti-inflammatory properties too.
FUN FACT: Inflammation is mostly caused by the response of our immune system. It’s a normal part of the healing process but if left unchecked, or if it becomes over active, that’s not good.
Vitamin D can reduce immune response and inflammatory markers. In this way, vitamin D helps to temper the immune response. Not to the point of suppressing it like potent anti-inflammatory drugs (steroids) but rather, vitamin D helps to keep the immune system in balance. This helps to support healing without the collateral damage that can come with too much inflammation (“cytokine storm”).
Supplement studies using vitamin D have found reductions in inflammatory markers in the blood. This helps with symptom management and disease progression, although not all studies agree.
Some researchers think vitamin D, due to its effects on the immune system, may also help with serious food allergies. A few small studies show that children with low vitamin D levels have an increased risk of food allergies. More research is needed.
Maintaining optimal levels of vitamin D has also been shown to lower the risk of colds and flu. Are you getting enough?
Cholecalciferol, a.k.a. vitamin D
Vitamin D and digestive diseases
Since vitamin D is fat-soluble, it’s absorbed along with fat in the diet. So, people who don’t eat or absorb enough fat are at risk of lower vitamin D levels. This can include people with many digestive issues such as celiac disease, inflammatory bowel diseases (IBD) like Crohn’s & colitis, as well as people who have had gastric bypass surgery.
Also, a healthy vitamin D status seems to go hand-in-hand with a healthy gut. For example, there is a link between sub-optimal vitamin D, gut microbiome status, gut inflammation, and diseases of the gut like IBD and colon cancer.
Vitamin D is involved in your gut barrier function. It is needed for the cells of your digestive tract to make tight junctions. These proteins help to keep the spaces between the cells of your gut sealed tight. If the tight junctions are faulty, food proteins, toxins, bacteria can enter your bloodstream and lead to poor health. This is called leaky gut but in the medical world, it’s called gut barrier dysfunction.
Vitamin D and cancer
It’s not just colon cancer that’s associated with low levels of vitamin D. Higher levels of vitamin D are associated with a lower risk for prostate, breast, bladder, lung, lymphoma, pancreatic, skin, ovarian, leukemia and other cancers.
In the lab, cancer cells don’t seem to do as well when exposed to higher levels of vitamin D. They don’t divide or invade other tissues as well; and, they seem to die easier. Vitamin D supports immune cells in their role to see out, and destroy developing cancer cells. By maintaining cell walls, they help to reduce the risk for cancer to spread. This is a new model of cancer development dubbed DINOMIT.
At this time, it’s unclear whether supplementing with vitamin D would reduce the risk of cancer in people so there’s no official recommendation. This is mainly because there’s a lack of well-designed studies to draw from. Most studies are very poorly designed but there are a few good ones. Some supplement studies have had positive results like the VITAL study, and a couple of studies looking at breast cancer.
Vitamin D and heart health
Several studies have linked low levels of vitamin D in the blood with heart disease. There are many overlapping mechanisms related to vitamin D and cardiovascular health including blood pressure, metabolic health like insulin resistance, diabetes, and metabolic syndrome.
Vitamin D may reduce the risk of and complications from arrhythmia and atrial fibrillation. Working with magnesium and vitamin K2, vitamin D helps to support blood vessel health. Vitamin D allows your body to absorb calcium, vitamin K2 puts the calcium in your bones and teeth and keeps it out of your blood vessels. Magnesium is needed to help vitamin D be converted to its active form as well; crucial for cardiovascular well-being.
Supplementing with vitamin D may help lower blood pressure slightly, but the evidence isn’t clear on how supplementing affects the risk of heart disease.
Vitamin D and blood sugar
Low levels of vitamin D during pregnancy have been shown to increase the risk of developing Type 1 diabetes in children. Maintaining vitamin D levels throughout pregnancy may reduce the risk for gestational diabetes as well.
Higher levels of insulin resistance have been found in those without adequate vitamin D in people without diabetes. Insulin resistance, or prediabetes, progresses slowly for years before Type 2 diabetes develops.
Supplementing with vitamin D has been shown to preserve beta cell function. Beta cells are pancreatic cells that produce insulin. In its active form, calcitriol, vitamin D up-regulates (turns on) the genes that are responsible for telling the beta cells to make insulin.
Maintaining ideal blood levels of vitamin D can improve insulin sensitivity and lower the risk for Type 2 diabetes. Those with Type 2 diabetes will find improved blood sugar control and may slow down the progression of the disease.
Vitamin D for mental and brain health
Many cells in key areas of the brain have vitamin D receptors. Here, vitamin D has a role in circadian rhythms and sleep, mood regulation, cognition, affecting the growth of nerve cells (neurons), and impacts the developing brain. Research is suggesting an impact on social behaviour and autism.
There is continued, growing evidence of the link between low blood levels of vitamin D and symptoms of depression and anxiety.
Some studies also show a link between low vitamin D levels and increased risk of Alzheimer’s and Parkinson’s diseases. Many think that if there’s a family history of these diseases or if they’ve had gene testing done and find they have these genes, there’s nothing they can do. This simply isn’t true, gene expression is influenced by variables like nutrients, including vitamin D. Optimizing your blood levels would be a great first step.
Vitamin D and fertility
Conception is an equal opportunity event. Most of the focus is on women but sperm quality is important and sperm is very susceptible to environmental factors like diet, smoking, alcohol, and vitamin D.
Vitamin D helps to maintain higher levels of testosterone in men which influences fertility. Vitamin D seems to help improve sperm quality, motility, and survival of sperm cells. Vitamin D also helps women’s fertility, especially with PCOS.
There is a sweet spot. Both too high (> 150 nmol/L) and too low (< 75 nmol/L) levels of vitamin D in the blood seem to be associated with infertility.
Forms of vitamin D
Many vitamins come in more than one form. With vitamin D, it comes in two different forms: D2 (ergocalciferol) and D3 (cholecalciferol). There are small differences in their chemical structure which, in turns, influences their biological potency.
FUN FACT: Both forms are activated the same way: to 25(OH)D and then 1,25(OH)D.
Vitamin D2 is the plant-based form, while vitamin D3 is from animals, and what’s produced in your skin with sun exposure. Both forms can help rickets.
However, vitamin D2 is less potent than vitamin D3; about 1/3 as potent. Vitamin D3 (from food, sun or supplements) is better at raising and maintaining blood levels of 25(OH)D. D3 also produces 2-3 fold greater storage of vitamin D than does equal amounts of vitamin D2.
PRO TIP: vegans can get a source of vitamin D3 from lichen. Do yourself a favour and go for that, don’t rely on D2 (hint plant-based milk alternatives).
Sources of vitamin D
There are three main sources of vitamin D – sun exposure, foods, and supplements.
Our skin contains “pre” vitamin D. When exposed to UVB rays from the sun, this “previtamin” is converted into vitamin D (calciferol). However, there needs to be enough UVB for this to happen. All you have to remember is that the UVB index HAS to be 3 or higher. This is why vitamin D levels decline in people throughout the winter.
The problem is that too much UV radiation can contribute not only to skin cancer but also to dryness and other cosmetic changes in the skin over time. There is a safe way to get sun exposure during ideal conditions for the purpose of vitamin D production, but this depends on skin complexion. Burning is always bad.
Foods with vitamin D
Vitamin D is not naturally found in very many foods. The best sources include fatty fish and fish liver oils. Some is also found in beef liver, some cheeses, and egg yolks. Animal sources contain the D3 form of the vitamin. Some is even already converted into 25(OH)D which is thought to be 5 times more potent than the regular D3 form.
Naturally occurring plant sources of vitamin D2 are some mushrooms that have been exposed to the sun. That’s about it. Further limiting this as a source, is that D2 is not as biologically active as D3.
Because it’s naturally found in so few foods, vitamin D is also added to certain foods. This is called “fortification.” In fact, fortified foods are the main source of dietary vitamin D in Canada and the US.
Fortification of food with vitamin D can improve vitamin D status in the population.
Some of these vitamin D fortified foods include milk, milk alternatives (soy, almond, hemp, etc), breakfast cereals, and yogurt. Check your labels to find out if yours has been fortified with vitamin D (it will be listed as an ingredient). Milk and yogurts are fortified with D3, milk alternatives, D2.
Infant formulas in Canada and the US are required to have at least 40 IU of vitamin D for each 100 kcal of formula.
FUN FACT: Because vitamin D is a fat-soluble vitamin, absorption from foods, drinks, and supplements is improved when taken at the same time as a fat-containing meal.
Vitamin D supplements
Vitamin D supplements come in both forms: D2 and D3. The plant-based D2 form is manufactured by exposing yeast to UV radiation. The animal-based D3 form is made from lanolin but there are also vegan sources of D3 from lichen.
If you are at risk for vitamin D deficiency, your health care provider can test your vitamin D level and recommend a course of action specifically for you.
However, if you don’t have a professional recommendation for how much vitamin D to take, the safest way to supplement is to follow the instructions on the label. Best not to take more than 4,000IU/day (100 mcg/day), unless told to by your licensed health care provider.
And don’t forget to check with your doctor and/or pharmacist if you’re taking medications because vitamin D supplements can interact with some of them.
It’s recommended that breastfed babies be supplement with vitamin D because breast milk tends to be low in vitamin D. Because the formula is fortified with vitamin D, formula-fed babies are essentially being supplemented. Speak with your licensed healthcare professional for recommendations.
Vitamin D deficiency
As mentioned, there are very few ways to get enough vitamin D. Studies show that between 30-96% of people simply don’t get enough. This deficiency is so common that some researchers have called it a “public health concern” and a “global problem.”
Vitamin D deficiency should really be defined by physiological needs. Even if it’s based solely on its indisputable role in bone health.
The fact of the matter is, calcium absorption is only optimized with vitamin D levels between 75-80 nmol/L (30 to 32 ng/L). PTH, which pulls calcium from your bones, is optimally suppressed at around 100 nmol/L (40 ng/L).
What’s curious, is that the Institute of Medicine (IOM), which Health Canada is part of, uses the following numbers:
- <30 nmol/L = deficient
- 30-50 nmol/L = insufficient
- 50-125 nmol/L = adequate
- 125+ nmol/L = high*
(*note, “high” doesn’t mean toxic or dangerous. Humans can easily achieve this and higher with safe sun exposure. 125+ is still considered within the normal physiological range).
The IOM and Health Canada state that 50 nmol is sufficient/adequate but they also acknowledge the fact that at 50 nmol, about 1/3 of the population will have osteoid tissue, a.k.a demineralized bone. This is because calcium isn’t being optimally absorbed by the gut and PTH is pulling it from bones.
Vitamin D deficiencies can happen when, over time, people aren’t getting enough safe sun exposure. Also, when they aren’t eating enough foods containing vitamin D and aren’t taking supplements. It can also happen if the vitamin D is not being absorbed very well, or if the kidneys have trouble converting the “previtamin” D into the active form 1,25(OH)D.
People who are more likely to be deficient in vitamin D include:
- Pregnant and lactating women, and breastfed infants
- Older adults
- People with limited sun exposure (including athletes who train indoors)
- People with darker skin
- People with digestion issues that prevent proper absorption (e.g. inflammatory bowel disease, celiac disease, etc.)
- People with obesity
- People who have undergone gastric bypass surgery.
How much vitamin D per day?
For adequate blood levels of 25(OH)D, how much vitamin D do you need to get every day?
To get enough vitamin D from the sun, a general rule is to get about 10–30 minutes of sun between 10:00 a.m. & 3:00 p.m. at least three to four times a week to the face, arms, legs, or back without sunscreen. Exposure time depends on complexion; the darker your skin, the longer you need.
In Canada and the US, the IOM has set target daily amounts when it comes to getting enough vitamin D from foods and supplements. This amount, called the “Recommended Dietary Allowance” (RDA), ensures that at least 97% of people get enough vitamin D every day. Those recommendations are:
- 10 mcg (400 IU) per day for infants under the age of one.
- 15 mcg (600 IU) per day for everyone aged 1-70 years old, including pregnant and lactating women.
- 20 mcg (800 IU) per day for everyone over the age of 70.
Here’s the rub though, these recommendations were meant to get people to the inadequate level of 50 nmol. Problem is, they use the incorrect statistical test to come up with this number. When this was pointed out, and they redid the analysis, the RDA for those 1 to 70 years of age should be much higher.
In their hubris, the IOM admitted this mistake but refused to change their recommendations of 600 IU per day for those over 1 year of age. Again, they only have the goal of 50 nmol/L in mind
The reality is, to get most of us between 50-75 nmol/L, we’d need to get a minimum of 2000 IU/day. More if your goal is 80 nmol for optimal calcium absorption. There may be hope, at least in the US.
Vitamin D in foods and supplements may be measured in both mcg (micrograms) and/or IU (international units). The conversion factor is 40 IU = 1 mcg.
Vitamin D has many health-promoting roles in the body. Most of the evidence is for bone health, but it’s also associated with a healthy immune system, digestive system, heart and mental health, blood sugar regulation, fertility, and resistance to cancer.
Vitamin D is also the most common deficiency.
We can get vitamin D from sun exposure, some foods, and supplements.
The best way to know how much vitamin D you need is to have your blood tested if you’re at risk. If you don’t have a test or professional recommendation, following the label directions on your vitamin D supplements can be a safe way to get enough.
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