Vitamin D is Vital for Health

Both a vitamin and a prohormone, vitamin D is vital for healthy bones and teeth. Indeed, it plays an essential role in the metabolism of calcium in the body. It regulates the level of blood calcium by improving the intestinal absorption of this mineral, while minimizing its elimination by the urine. It also participates in the deposition and removal of calcium from bones, as needed by the body. “Calciferol”, one of the other names for vitamin D, comes from Latin and means “who carries calcium”.Vitamin D has also been called “antirachitic vitamin” because rickets, a growth disorder, is caused by a vitamin D deficiency. In North America, as well as in several industrialized countries, small amounts of vitamin D in milk and margarine in order to prevent this disease.

Vitamin D actually includes a set of fat-soluble substances that are sometimes called provitamins D. These provitamins include ergocalciferol (D2 – plant form) and cholecalciferol (D3 – animal form). The body partially transforms them into calcitriol (in hormonal form), the compound that generates most of the beneficial effects. Calcitriol also controls many genes that regulate, for example, cell proliferation and differentiation and the secretion of insulin9. It is therefore becoming increasingly evident that vitamin D plays a role that goes far beyond the health of bones and teeth.

The body can directly synthesize vitamin D through the skin, which is why it cannot be considered strictly or purely as a vitamin. Under the effect of the sun’s ultraviolet rays (hence the name “vitamin sun”), our body produces cholecalciferol (vitamin D3) which after passing to the liver and then the kidney takes its active form (calcitriol).

Vitamin D is a special case among nutrients and drugs. Indeed, it can accumulate in fats and the liver where it is stored. Depending on the needs of the body, it can be metabolized and put back into circulation.

Certain efficiency

Treat hypoparathyroidism, psoriasis and rickets.

See the legend of the symbols

Likely effectiveness

Prevent dental caries and falls in people at risk.

Likely effectiveness

Prevent osteoporosis and slow its progression in people over 50 (in combination with calcium).

Uncertain effectiveness

Prevent certain cancers, type 1 and type 2 diabetes, certain other autoimmune diseases (multiple sclerosis, inflammatory bowel disease, etc.) and cardiovascular disorders. Boost immunity.

Vitamin D dosage
Vitamin D dosage is often given in international units (IU) rather than micrograms (µg). To find your way around, just know that 1 µg (1 millionth of a gram) is equivalent to 40 IU.

Prevention of osteoporosis

Osteoporosis Canada Recommendations

For healthy people under 50:
a supplement of 400 IU to 1,000 IU (10 to 25 µg) of vitamin D per day and a dietary intake of calcium of 1,200 mg, to be supplemented with a supplement, if necessary.
For people aged 50 and over:
a supplement of 800 IU to 2,000 IU (20 to 50 µg) of vitamin D per day and a dietary intake of calcium of 1,200 mg, to be supplemented with a supplement, if necessary.
Osteoporosis treatment (for people with osteoporosis)

Osteoporosis Canada Recommendations

from 800 IU to 2,000 IU (20 to 50 µg) of vitamin D per day as a supplement (the optimal dosage is determined by the attending physician) and a dietary intake of calcium of 1,200 mg, to be supplemented by a supplement, if needed.

To be effective, vitamin D and calcium intake must be continuous.
The diagnosis and treatment of osteoporosis is the result of medical monitoring.
Vitamin D can be taken at any time of the day: during, before, after or between meals.
As it seems that the body cannot absorb more than 500 mg of calcium at a time, it is recommended to take the supplements in doses of 500 mg or less, 2 or 3 times a day, with meals.
Cancer prevention

The Canadian Cancer Society recommends a supplement of 1,000 IU (25 µg) per day of vitamin D in the fall and winter. Adults who are at higher risk for vitamin D deficiency should do the same throughout the year: the elderly, those with dark skin pigmentation, who do not go outdoors or who wear clothing covering the major part of their body.
Several experts believe that the position of the Canadian Cancer Society, although it is an improvement over that of Health Canada, remains too conservative with regard to scientific evidence. Instead, they recommend a daily dosage of 2,000 IU to 4,000 IU of vitamin D3. In summer, the dose could be reduced, provided you expose yourself to the sun regularly (without sunscreen, but without sunburn).

Sun and vitamin D

It is estimated that sun exposure can provide 80% to 90% of the vitamin D required. A simple exposure (without sunscreen) of the hands, forearms and face for 10 to 15 minutes (at the latitude of Toronto) between 11 a.m. and 2 p.m., 2 or 3 times a week, would be enough to ensure adequate intake for a healthy adult, 10 approximately from April to October. This is an average: the exposure time required to get enough vitamin D also depends on the skin type, the intensity of the rays (UVB index), and the basal level of vitamin D in the blood.11,12 For example, people with dark skin, those who expose themselves before 11 a.m. or after 2 p.m., those who systematically use sunscreen and those who live in more northern latitudes must be exposed longer, or more often , to obtain an adequate supply of vitamin D. For example, people with dark skin must be exposed to 3 to 5 times longer than others95.

Note. Since prolonged exposure to the sun can cause skin cancer, experts recommend the use of sunscreens with a sun protection index of at least 15 as soon as you are exposed for more than 15 minutes.

1. Less sun exposure: According to a survey by the National Institutes of Health, people with a higher education level tend to spend less sun exposure in their lifestyles, and attach importance to skin whitening and sun protection, resulting in even indoor sports or layers of sun protection measures Next, vitamin D cannot be synthesized by UVB in ultraviolet light.

2. Biliary tract diseases: Vitamin D belongs to fat-soluble vitamins, which must be digested through bile. If there is biliary tract disease that leads to insufficient secretion of bile, it will affect the absorption of these fat-soluble vitamins and cause disease.

3. People with poor gastrointestinal or gastric bypass surgery: those with poor gastrointestinal tract have poor fat absorption, which also makes the conversion and absorption rate of vitamin D not high, so they are also prone to lack of vitamin D; and those who have undergone gastric bypass surgery , Lack of the process of absorbing fat in the upper part of the small intestine will affect the absorption rate of vitamin D.

4. Poor liver and kidney function: Vitamin D itself has no biological function, and it must be transformed into a chemical structure that can be used by the body after being metabolized by the liver and kidney to exert its biological function.

5. Obese: For people with a BMI value greater than 30, subcutaneous fat will prevent the release of vitamin D into the blood circulation, and the concentration of vitamin D precursors in the blood will be lower than that of normal-weight people, that is, obese people need to add more vitamins D.

6. Elderly: Because of the aging factors, the elderly are less effective than young people in synthesizing vitamin D. If they do not have enough dietary intake and go out and spend less time in the sun, they are prone to lack of vitamin D.

7. Dark skin: The basal layer and spinous layer of the epidermis are the locations where melanin absorbs ultraviolet rays and synthesizes vitamin D. People with dark skin have more melanin in the epidermis that absorbs the ultraviolet energy used to synthesize vitamin D, so it can be The reduced energy of synthetic vitamin D also easily causes vitamin D deficiency.

How to supplement vitamin D?

Dr. Jiang Kunjun, the author of “One Day D: Vitamin D Helps You Take Care of Your Health,” said that about 80 to 90% of vitamin D can be obtained by exposure to the sun; and about 10 to 20% of vitamin D can be obtained by ingesting food. Therefore, most of the vitamin D available in the human body is synthesized by sun exposure. How can the sun be good?

How can it be easier to help vitamin D synthesis in the sun?

The UVB of ultraviolet rays in sunlight is the key to help the body synthesize vitamin D, but it cannot penetrate ordinary glass, so it is not possible to synthesize vitamin D in the sun through the glass, but people will cause skin due to the UVA light that penetrates the glass. Aging; and when the sky has a cloud or air pollution alarm, it will reduce UVB by 50 ~ 60%. In order to allow UVB in the sun to synthesize vitamin D in the human body, it is recommended to expose the face, arms, legs or back to the sun for 5 to 30 minutes at 9 to 10 am or 3 to 4 pm.

According to research, sunscreen products with an SPF greater than 8 will isolate the skin from synthesizing vitamin D, but most people will not completely apply sunscreen products to the skin, so they can still synthesize vitamin D. It is recommended that people choose a moderate SPF factor of about 10 when sunbathing The sunscreen of ~ 15 can both block UVA and help absorb UVB to synthesize vitamin D.

What are the vitamin D of food sources?

The food-derived vitamin D is divided into animal-derived vitamin D3, such as sardines, salmon, cheese, egg yolk; plant-based vitamin D2, such as black fungus, soybeans, mushrooms, grains, etc. Although many claims have pointed out that animal foods have better vitamin D3 than plant foods, vitamin D2, but the American Endocrine Society ’s treatment guidelines for vitamin deficiencies, have found from clinical trials that regardless of vitamin D2 or D3, the body ’s absorption and utilization The rates are almost the same, and all can be used as a source of vitamin D3 supplements. When taking supplements, they should be combined with fat intake to help absorption.

Nutritional supplement

People who do n’t want to sunbathe and ca n’t supplement vitamin D from foods are advised to choose appropriate supplementary health foods. When choosing, please choose health products, dosage forms and safety that have passed the review of the Ministry of Health and Welfare and obtained official license documents and passed the content and quality safety certification Sex is recommended by professional doctors and pharmacists to achieve the essential meaning of preventive health care.


UI *

µg **

0 to 1 year

400 IU ***

10 µg ***

1 year to 70 years

600 IU

15 µg

over 70

800 IU

20 µg

Pregnant and breastfeeding women

600 IU

600 IU

Source: Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D, 2010. These data are the result of a consensus between Canadian and American authorities.
* international unit
** 1 microgram = 1 millionth of a gram
*** In the absence of sufficient scientific data, the IOM fixed, not a recommended nutritional intake (ANR), but an adequate intake (AS). Adequate vitamin D intake is based on the average intake observed in healthy North American babies.


Even if the recommended nutritional intake of vitamin D was tripled in November 2010 by the American and Canadian authorities1 (table above), several researchers still find it far too low. They suggest increasing it to at least 2,000 IU to decrease the incidence of diabetes, cancer and cardiovascular disease2. To learn more about this controversy, see the Vitamin D Research section.

How to take vitamin D supplements
Weekly or monthly dosage. To ensure an adequate intake, it is not necessary to take a vitamin D tablet every day. It is perfectly possible, as long as one chooses a liquid supplement, to take a weekly or even monthly dose. It is an increasingly common medical practice, especially among the elderly who already take a number of medications on a daily basis.

According to Dr. Reinhold Vieth, of Mount Sinai Hospital in Toronto, vitamin D3 in liquid form should be used because it is not certain that tablets or capsules taken in large quantities dissolve properly . This would result in an insufficient dosage, part of the vitamin being eliminated in the stool before being metabolized3. Vitamin D3 in liquid form is available over the counter in pharmacies and health food stores.

Dr. Vieth specifies that “several of these products, duly approved by Health Canada, are currently available. There are some that contain up to 1,000 IU per drop. By mixing them in the required amount with their food, it is easy to take a weekly (7 drops or 7,000 IU) or monthly (30 drops or 30,000 IU) dose ”. It is also important, according to Dr. Vieth, to choose a supplement that contains only vitamin D, not a mixture of vitamin D and calcium or a multivitamin supplement, for example3.

Studies published to date have demonstrated the efficacy and safety of such a practice. In some trials, even annual doses of vitamin D have been given without any side effects, but it appears to be more effective to stick to a bimonthly dosage (every 2 months) or less (monthly or weekly) to ensure a constant supply 7.

Food sources of vitamin D
For a more complete list of sources of vitamin D, see the Vitamin D Nutrient List.



Vitamin D*

Salmon, grilled or poached

100 g (3 ½ oz)

600-920 IU

Canned salmon

100 g (3 ½ oz)

320-760 IU

Grilled bluefin tuna
Marinated Atlantic herring

100 g (3 ½ oz)

280 IU

Grilled trout

100 g (3 ½ oz)

200-280 IU

Cow milk, 0% to 3.25% fat

250 ml (1 cup)

120 IU

Fortified soy beverage

250 ml (1 cup)

80 IU

* 1 µg = 1 microgram = 40 IU


Vitamin D deficiency
Note. In this sheet, the term “blood vitamin D level” designates the level of 25 hydroxycholecalciferol (25 (OH) D) in the blood.

The medical authorities in Canada and the United States have set the blood vitamin D level adequate for good bone health at 50 nanomoles per liter (nmol / l). According to data collected by Health Canada, 90% of Canadians aged 6 to 79 reach this rate and only 4% are deficient13.

These data are however strongly contested by many experts (see the Research section). The most recent Canadian study even established that 25% of the population has a blood vitamin D level below 50 nmol / l in winter19. In people not taking a vitamin D supplement, 37% have a winter rate of less than 50 nmol / l. This proportion doubles for Canadians with dark skin. This study involved 5,306 people aged 6 to 79 living across Canada. Several surveys have been carried out in Quebec, Canada and Europe. The results clearly established that a significant proportion of the population living in northern latitudes is deficient in vitamin D, when the minimum blood level is set at 75 nmol / l14-18.
Too little exposure to the sun can cause a vitamin D deficiency. This is often the case in winter.