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Anxiety Has Left the Building, Vitamin B1 has arrived
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So you have heard about the wonderful health benefits of vitamin D supplements and are now shopping, scrolling your way through the endless list of options online. Your screen fills with a bewildering variety of available products, and you may wonder: Why is it vitamin D3, and not simply D? And what does IU mean? Is it the higher the IU, the better the supplement? In this blog, we give you a few pointers so that you can make an informed decision about your vitamin D supplementation…
Just like with vitamin B, there exist several different forms of vitamin D—five, to be exact. In terms of their chemical composition, all the different vitamin D forms are secosteroids, a sub-class of steroids with one broken bond of steroid rings.
For our purposes, vitamin D2 and D3 are the most important forms. Both promote the absorption of calcium in your gut, which in turn regulates and promotes bone growth, and they support your immune and neuromuscular systems. The chart below shows their characteristics in greater detail:
| Vitamin D2 | Vitamin D3 | |
| Also known as… | Ergocalciferol | Cholecalciferol |
| Can the human body produce it? | No | Yes, within the human skin, from 7-dehydrocholesterol, when activated by sunlight |
| From which (nutritional) sources can you get it? | Fungi grown in UV light Dietary supplements Foods fortified with vitamin D | Oily fish (salmon, sardines, etc), Fish oil, Egg yolk, Liver, Butter, Dietary supplements, Foods fortified with vitamin D |
| How is it manufactured for use in supplements and fortified foods? | Yeast is exposed to UV light to convert ergosterol into ergocalciferol | 7-dehydrocholesterol from lanolin (an oily substance found in sheep’s wool, for example) is exposed to UV light |
| How effectively can it raise your vitamin D level? | Less effective at higher doses | Very effective |
Your body can produce vitamin D3 when it is exposed to sunlight; therefore, it is also called the “sunlight vitamin.” Vitamin D2, however, needs to come from your diet. Most fortified foods contain greater amounts of vitamin D2, partially because it is cheaper to produce; however, this form is of lower quality and tends to degrade more easily.
If you want to raise your vitamin D level, look for D3, as this form has been proven to be better absorbed and more effective for this purpose.[1]
IU stands for International Unit. This unit of measurement is used for biologically active substances such as vitamins, hormones, vaccines, medications and the like. The basis for determining this unit of measurement is not mass or volume, but the biological effect. For example, in terms of the effect vitamin A has in your body, 0.3 micrograms of vitamin A in the form of retinol equals 0.6 micrograms vitamin A in the form of beta-carotene, and therefore 1 IU of beta-carotene weighs twice as much as 1 IU of retinol. This unit of measurement is employed by the World Health Organization (WHO) to ensure that we do not compare apples and oranges, but apples and apples when it comes to figuring out how effective supplements and medications are.
For vitamin D3, 1 IU equals 0.025 micrograms. For instance, one tablespoon of cod liver oil contains 1,360 IU, or 34 micrograms. Vitamin D supplements are available in a large range of IU, from 400 to 50,000.
You should be aware that a higher amount of IU does not necessarily mean more benefits, for three reasons. First, excessive doses of vitamin D have been linked to excess calcium in the body (hypercalcemia), which can then cause painful kidney stones.[2] As with most things in life, moderation is key. Secondly, whether you choose vitamin D2 or D3 will make a difference. In other words, vitamin D3 will give you more bang for your buck, even at lower amounts of IU. Thirdly, your vitamin D3 supplement’s other ingredients also play an important role in how effectively your body can process this important micro-nutrient.
All forms of vitamin D are fat-soluble. This means that not only are they more likely to occur in oily substances (such as salmon and butter), but they also more easily dissolve in fats and oils. In other words, vitamin D’s bioavailability—the rate at which it is absorbed into your blood stream to take full effect on the cellular level—is much greater when you take it together with some type of fat or oil.
One of the most well-known roles of vitamin D is its ability to enhance calcium absorption in the gut, which is vital for maintaining healthy bones. Without sufficient vitamin D, the body cannot effectively absorb the calcium necessary for bone formation, leading to weaker bones and an increased risk of fractures.
Vitamin D deficiency is a primary cause of rickets in children, a condition characterized by soft, weak bones that can lead to bone deformities. In adults, prolonged deficiency can result in osteomalacia, which causes bone pain and muscle weakness. Moreover, low vitamin D levels are a significant risk factor for osteoporosis, a condition that causes bones to become brittle and more prone to fractures, particularly in older adults.
Ensuring that you have adequate vitamin D—whether through diet, sunlight, or supplementation—is crucial for maintaining bone density and reducing the risk of these bone-related disorders.
Vitamin D is not just essential for bone health—it also plays a crucial role in maintaining a strong immune system. Research has shown that vitamin D can enhance the pathogen-fighting effects of monocytes and macrophages—white blood cells that are important parts of your immune defense—and decreases inflammation. This is why a deficiency in vitamin D is associated with an increased susceptibility to infections, including the flu, colds, and respiratory tract infections.
Several studies suggest that adequate vitamin D levels may reduce the risk of chronic diseases, such as cardiovascular disease and autoimmune conditions like multiple sclerosis. Vitamin D helps modulate the immune response, ensuring that it is neither too weak to fight off pathogens nor so strong that it attacks the body’s own tissues, as seen in autoimmune diseases. For those living in regions with limited sunlight, especially during winter months, maintaining healthy vitamin D levels through supplementation could be particularly important for immune health.
Vitamin D deficiency is more common than many people realize and can have serious health consequences if left unaddressed. One of the most significant risks of low vitamin D levels is its impact on bone health, leading to conditions like osteoporosis and osteomalacia. However, the risks extend beyond just bone health.
Low vitamin D levels have been linked to an increased risk of cardiovascular disease, including hypertension and heart failure. There is also growing evidence that vitamin D deficiency may be associated with mental health issues such as depression and seasonal affective disorder (SAD). Additionally, insufficient vitamin D has been connected to impaired immune function, increasing the likelihood of infections and potentially contributing to the development of autoimmune diseases.
People at higher risk for vitamin D deficiency include those with limited sun exposure, individuals with darker skin, older adults, and those with certain medical conditions that affect fat absorption, such as Crohn’s disease or celiac disease. Recognizing the symptoms of vitamin D deficiency—such as fatigue, bone pain, muscle weakness, and mood changes—is crucial for early intervention and prevention of these health risks.
The most efficient way to obtain vitamin D is through sunlight. When your skin is exposed to UVB rays from the sun, it synthesizes vitamin D3, which is then converted into its active form in the body.
However, several factors influence how much vitamin D you can produce from sunlight. Geographic location plays a significant role—people living farther from the equator may not get enough UVB exposure, especially during the winter months. Skin type is also a factor; those with darker skin have more melanin, which can reduce the skin’s ability to produce vitamin D. Age can affect synthesis as well, with older adults producing less vitamin D than younger individuals.
In addition to sunlight, certain foods can help you maintain healthy vitamin D levels. Fatty fish like salmon, mackerel, and sardines are excellent sources, as are egg yolks, beef liver, and fortified foods like milk and cereals. Incorporating these foods into your diet, along with moderate sun exposure, can help you naturally maintain sufficient vitamin D levels.
When it comes to vitamin D supplementation, it’s essential to consider individual needs, which can vary based on age, lifestyle, and existing health conditions. The recommended daily allowance (RDA) for vitamin D varies, with most health organizations suggesting 600-800 IU for adults. However, some individuals, such as older adults, those with limited sun exposure, or individuals with certain medical conditions, may require higher doses.
It’s also important to note that vitamin D is fat-soluble, meaning it is better absorbed when taken with a meal that contains fat. Many vitamin D supplements are already formulated with oil to enhance absorption, but taking your supplement with a meal is still beneficial.
Although high doses of vitamin D are available, it’s crucial to avoid excessive intake. The upper limit for daily vitamin D intake is generally set at 4,000 IU for adults. Taking too much vitamin D can lead to hypercalcemia, a condition characterized by elevated calcium levels in the blood, which can cause nausea, weakness, and kidney stones. It’s always best to consult with a healthcare provider to determine the appropriate dosage for your specific needs, especially if you have any underlying health conditions or are taking other medications.
Have we answered your vitamin D supplement questions? Make sure to consult with your healthcare provider to find the supplement that is best suited to your needs… and happy (informed) shopping!
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Sources
- Arnarson, Atli, PhD, “Vitamin D2 vs. D3: What’s the Difference?” Healthline, https://www.healthline.com/nutrition/vitamin-d2-vs-d3
- Brown, Jessica, “Should Everyone Be Taking Vitamin D?” https://www.bbc.com/future/article/20181010-do-vitamin-d-supplements-work
- “Calcium and Vitamin D,” National Osteoporosis Foundation, https://www.nof.org/patients/treatment/calciumvitamin-d/
- Somerville, Judson, MD, The Optimal Dose: Restore Your Health with the Power of Vitamin D3. Big Bend Press, 2018.
- “Taking Too Much Vitamin D Can Cloud Its Benefits and Create Health Risks,” Harvard Health Publishing, https://www.health.harvard.edu/staying-healthy/taking-too-much-vitamin-d-can-cloud-its-benefits-and-create-health-risks
- Tripkovic, Laura et al. “Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis.” The American Journal of Clinical Nutrition vol. 95,6 (2012): 1357-64. doi:10.3945/ajcn.111.031070
- “Vitamin D: Fact Sheet for Health Professionals,” National Institutes of Health: Office of Dietary Supplements, https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h8
[1]Laura Tripkovic et al. “Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis.” The American Journal of Clinical Nutrition vol. 95,6 (2012): 1357-64.
[2]“Vitamin D: Fact Sheet for Health Professionals,” National Institutes of Health: Office of Dietary Supplements, https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h8; “Taking Too Much Vitamin D Can Cloud Its Benefits and Create Health Risks,” Harvard Health Publishing, https://www.health.harvard.edu/staying-healthy/taking-too-much-vitamin-d-can-cloud-its-benefits-and-create-health-risks
