Vitamin D or calciferol is a fat-soluble vitamin essential for the maintenance of good health and the prevention of disease. What are our vitamin D needs? When should we supplement? The basics of vitamin D.
What are the benefits of vitamin D?
Vitamin D increases the intestinal absorption of calcium and phosphorus. It thus plays a role in the solidity of bones and teeth.
It also contributes to the proper functioning of the muscles and in particular the heart muscle. Vitamin D also contributes to the normal functioning of the immune system.
“Studies still in progress suggest that vitamin D would also have other properties: it could have a role in type 2 diabetes, obesity, metabolism in general, and certain types of cancer.
This is well demonstrated on cellular and animal models but this is less clear in humans”, explains Top Santé, Jean-François Landrieu, Research Director, Human Micronutrition team of the Cardiovascular and Nutrition Research Center (C2VN), INRAE Marseille.
Note that in 2019, more than 70% of French adults had insufficient vitamin D intake or even a deficiency in 6.5% of cases.
What are our vitamin D needs?
Vitamin D requirements according to age are:
- Infants over 6 months: 10 µg/d per day
- Infants 6 months and older: 10 µg/d per day
- Children from 1 to 3 years old: 15 µg/d per day
- Children 4 to 10 years old: 15 µg/d per day
- Teenagers 11 to 17 years old: 15 µg/d per day
- Men and women aged 18 and over 15 µg/d per day (i.e. 600UI)
- Pregnant or breastfeeding women: 15 µg/d per day
Source: nutritional references in vitamins and minerals, ANSES
You should know that vitamin D comes mainly from diet and exposure to the sun.
Who needs vitamin D supplementation?
In children, vitamin D is essential for bone growth. To ensure this growth, vitamin D is prescribed in France from the first days of life to prevent rickets, and until the age of 18. Vitamin D is most commonly given as drops (Adrigyl, Zyma D, Pediakid ) to infants.
From 18 months to 5 years, and in adolescents (10 to 18 years), the French Society of Pediatrics (SFP) recommends a quarterly loading dose of 80,000–100,000 IU at the beginning and end of winter ( in the form of an ampoule ).
For adults, supplementation is necessary:
- for everyone, during periods with little sunshine (autumn and winter)
- in the elderly, men, and women, especially when they go out little, the lack of sun decreases the reserves of vitamin D
- in people who get little exposure to the sun
- in people with dull or dark skin in whom the synthesis of this vitamin by exposure to the sun is less effective.
- in postmenopausal women
- in pregnant women, in the third trimester
“We are unable to cover our vitamin D needs with dietary intake because there are not many food vectors and also because many parameters mean that the synthesis of vitamin D through sun exposure is not extraordinary: almost zero syntheses for people on the North Latitude for long months, pollution which acts as an anti-UVB filter, skin phototype, sedentary lifestyle, use of sun protection…”, specifies Jean-François Landrier.
Vitamin D supplementation appears all the more important during the Covid-19 pandemic. A vitamin D deficiency could be associated with a greater risk of developing Covid and vitamin D insufficiency could constitute an independent risk factor for a severe form of Covid-19 (the studies are in progress, without an obvious scientific demonstration to this day).
The National Academy of Medicine (press release of May 22, 2020) recommends “rapidly measuring the serum vitamin D level (i.e. 25 OHD) in people over the age of 60 with Covid-19, and to administer, in the event of a deficiency, a loading dose of 50,000 to 100,000 IU which could contribute to limiting respiratory complications and to provide vitamin D supplementation of 800 to 1000 IU/day in people under the age of 60 years from the confirmation of the diagnosis of Covid-19”.
“In any case, you must not be in a situation of insufficiency or deficiency in vitamin D compared to all its other biological functions”, indicates Jean-François Landrier.
Do vegetarians and vegans have vitamin D deficiencies?
Vegans or vegetarians who do not consume meat, fish, dairy products or eggs, appear to be at greater risk of having vitamin D deficiencies because they do not consume the foods richest in vitamin D. “However, a study showed that vegans were no more deficient in vitamin D than non-vegans, probably because they supplemented with vitamins”, underlines Jean-François Landrier.
Where is vitamin D found?
Vitamin D is a special fat-soluble vitamin because it is synthesized by our skin under the action of sunlight.
The vitamin D thus created represents approximately 50% to 70% of the total vitamin D intake (this intake being controversial and perhaps much lower according to some specialists) while the rest comes from our diet.
At the level of the deep layers of the skin, we find the precursor of vitamin D, pre-vitamin D. Under the action of UVB radiation, it is transformed into vitamin D.
Exposing yourself to the sun for 15 to 20 minutes at the end of the morning or in the afternoon provides the body with an adequate daily supply of vitamin D.
What foods are rich in vitamin D?
Vitamin D comes in two forms: cholecalciferol (vitamin D3) in foods of animal origin and ergocalciferol (vitamin D2) in those of vegetable origin. Foods rich in vitamin D are :
- Cod liver oil,
- fatty fish (such as herring, sardines, and salmon),
- the egg yolk,
- certain mushrooms (chanterelles or chanterelles, shiitake mushrooms),
- dark chocolate,
- dairy products (butter, margarine, Emmental type cheese).
What are the signs of vitamin D deficiency?
Vitamin D deficiency is defined by a circulating concentration of 25-hydroxyvitamin D, or 25(OH)D, of less than 10ng/mL (or 30nmol/L), and vitamin D insufficiency is defined by a concentration circulating 25(OH)D between 10 and 20ng/mL (or 50nmol/L).
Symptoms of vitamin D deficiency are rickets (skeletal disease) in children and osteomalacia (bone decalcification) in adults, which are due to impaired bone mineralization due to reduced absorption of dietary calcium and phosphorus.
Vitamin D deficiency leads to a decrease in bone mineral density which predisposes the elderly, especially postmenopausal women, to osteoporosis.
Is vitamin D available without a prescription?
It is possible to find vitamin D without a prescription, in the form of food supplements ( capsules, tablets, drops ) in pharmacies or on the internet, but it is not recommended to self-medicate! “You have to be careful with the doses of vitamin D which can be high or even very high in these food supplements with a risk of putting yourself in excess of vitamin D.
It is not a trivial molecule”, explains Jean-François Landrier.
It is better to consult your doctor who will prescribe you vitamin D in the form of an ampoule or a drop, following the recommendations according to age. This is then covered by Social Security.
What dosage? What to do in case of overdose?
If you want to take vitamin D supplements, at least ask your pharmacist for advice so as not to risk an overdose, which is rare, but can have significant health consequences. Since vitamin D is fat-soluble, it can actually accumulate in the body.
Vitamin D poisoning is rare but can be caused by daily supplementation in too high doses. In case of excessive supplementation, hypercalcemia (increased urinary calcium excretion) and various disorders (headaches, nausea, vomiting, weight loss, intense fatigue) can be observed.
These symptoms disappear fairly quickly when the supplementation ceases. Read also: vitamin D in babies, beware of the risk of overdose.
Sources :
- Interview with Jean-François Landrier, Research Director, Human Micronutrition team at the Cardiovascular and Nutrition Research Center (C2VN), INRAE Marseille.
- Vitamin D sheet, Eurofins-Biomnis Laboratories
- Jean-Claude Souberbielle, The non-classical effects of vitamin D: level of evidence and perspectives, MCED n°86 – January 2017
Image Credit: Photo by Vitolda Klein on Unsplash
