Vitamin D and Nutrition

Vitamin D in brief

Insufficient vitamin D is associated with an increased risk for depression, cardiovascular disease, respiratory tract infections, type 2 diabetes, and an increased risk of birthing complications. Needless to say, vitamin D has many important roles.

One other vital function this vitamin plays is in bone health. Vitamin D helps to increase the absorption of calcium in the gut, regulate calcium levels in the blood, and decrease calcium loss in the urine if levels of this mineral are low. To learn more about calcium and how much we need, see our calcium article.

Vitamin D recommendations

International Units (IU), as well as micrograms (mcg), are both units of measure used to describe amounts of Vitamin D. To convert IU to mcg, simply divide by 40. The recommendations for vitamin D are:

• Adults < 71 years: 600 IU (15 mcg) daily.
• Adults > 71 years: 800 IU (20 mcg) daily.
• Tolerable Upper Intake (maximum): stay below 4000 IU/day (100mcg/day) from combined food + supplement ​unless under medical supervision.

​For optimal health, some experts recommend 1000 to 2000 IU (25 - 50 mcg) of vitamin D2 or D3 daily.

Vitamin D sources

There are three common sources: sun, food and supplements. Let's explore each of these in more detail.

Sunshine

Our bodies can use the sun's rays, or ultraviolet light, to convert inactive vitamin D into its active form when the sun comes in contact with our bare skin. There are quite a few things we need to consider, though:

• Location on earth: in some places closer to the equator, 10 - 15 minutes of whole-body exposure in the mid-day summer sun is equivalent to taking 15,000 IU (375 mcg) Vitamin D3 orally. In countries like Canada, 30 minutes or less is needed to make 1000 IU (25 mcg) Vitamin D3 in summer months, and about 60 minutes is needed in the spring. In the fall and winter months, the sun's rays are inadequate to meet the needs of most. Depending on where we live, the intensity of the sun can differ, especially at different months of the year.
• Skin exposure to the sun: our skin needs to be bare for the UV rays to penetrate it. This means no clothes and no sunscreen. Otherwise, insufficient vitamin D is produced by the body.
• Skin colour: darker pigmented skin is less efficient at converting vitamin D to the active form. Longer exposure to the sun is required for those of us with darker skin compared to those with more fair skin.
• Age: the efficiency of vitamin D conversion in our bodies decreases with age.

Food sources

Although animal products such as milk, egg yolks and certain types of fish offer vitamin D, they do not offer it in amounts that are sufficient to meet recommended needs on a daily basis. This is also true for plant-based sources such as fortified non-dairy beverages, which offer only about 100 IU (2.5 mcg) vitamin D per 250 mL serving. Overall, vegan and non-vegan food sources are insufficient to meet our vitamin D needs.

Supplements

In a city like Vancouver, Canada, the sun's rays are only strong enough for our bodies to make vitamin D between April and September. During the other months, supplements are needed. Depending on where we live, supplements may not be needed if we're exposed to an adequate amount of sun for 15-60 minutes a day, with some skin exposed. See a dietitian or doctor for more information about this.

Types of vitamin D supplements

Vitamin D supplements come in two forms: vitamin D3, also known as cholecalciferol, and vitamin D2, also known as ergocalciferol. Vitamin D3 is usually derived from sheep's wool exposed to UV light, but plant-based options made from lichen are available. Plant-based vitamin D3 can be rather expensive and difficult to find though. Vitamin D2 is made when yeast is exposed to ultraviolet light, so it's always a plant-based source.

Important notes regarding supplementation

Effectiveness: research comparing the two types of vitamins shows that vitamin D2 tends to be less potent. This means larger doses may be needed to achieve the same effect. It's generally safe to supplement with 1000 to 2000 IU, or 25 - 50 mcg, of vitamin D2 or D3, although it's best to speak with a physician before beginning any new supplementations.

Individuals in the obese category: We recognize that weight can be a very personal topic for many of us. Weight is not necessarily the best indicator of health, but research indicates that individuals that fall into the obese category are at a greater risk for insufficient vitamin D. This is believed to be due to the extra fat cells that store the vitamin D. Although many possible mechanisms for why this deficiency is observed have been reported.

Multivitamins: remember that these can also contain vitamin D. Consider this when calculating total intake.

Timing of consumption: vitamin D is best absorbed with fat-containing foods. For optimal absorption of vitamin D, supplements can be taken with food.

Supplement type: there is no difference in the absorption of vitamin D supplements if they are liquid, chewable, or tablets.

Side effects: taking too much vitamin D in the form of supplements can cause too much calcium to be absorbed. Over several weeks or months, this can cause calcium to deposit in our arteries, which hardens them. This may increase the risk of cardiovascular events. Too much sun exposure hasn't been shown to have this effect.

Summary

1. Vitamin D from foods and sun exposure typically aren't enough to meet daily requirements. It's still important to enjoy foods with vitamin D, though.
2. Various factors impact our ability to get vitamin D from sunlight, such as location on the earth, skin exposure, skin pigmentation, and age.
3. Supplements come in 2 types: vitamin D2 as a plant-based source, and vitamin D3 which isn't always a plant-based source.
4. If supplements are needed, a vitamin D supplement that offers a minimum of 400 IU is usually enough. Taking supplements that offer up to 1000 IU is generally safe as well. For those of us following a plant-based lifestyle, it's recommended to choose vitamin D2 or plant-based D3 and take 1000 to 2000IU.

Want to learn more?

Vitamin D plays an important role in supporting good bone health. Learn more in our other PUL articles about how poor bone health can lead to more severe cases such as osteoporosis, or how calcium contributes to our bone health.