FAQ про вітамін D

FAQs About Vitamin D

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Updated July, 2018

By Reed Mangels, PhD, RD

Vitamin D has been in the news a lot lately. Researchers are looking at whether it plays a role in a multitude of diseases ranging from multiple sclerosis to depression to cancer. Vitamin D has long been known to be important for bone health and is being added to foods like orange juice and to many brands of calcium supplements. Vitamin D has always been looked on as an unusual vitamin because, unlike any other nutrient, our bodies can actually make a substantial amount of vitamin D. Add in the fact that it acts more like a hormone than a vitamin, and you can see why there's a lot to know about vitamin D.

We've recently heard from several readers who have had their blood checked for vitamin D and were surprised to learn that they were considered vitamin D deficient. They wrote asking us about vegan sources of vitamin D, the role of sunlight exposure, and what kind of supplements to use. We realized that it's a good time to answer some questions about vitamin D.

What Does Vitamin D Do?

Vitamin D is best known for its role in bone health - it helps our body absorb calcium. When vitamin D is deficient, we absorb very little calcium. That's the main reason that calcium supplements often also contain vitamin D. If calcium is not absorbed due to a vitamin D deficiency, the result is weaker bones that are more likely to fracture.

Studies also suggest that older people with lower blood levels of vitamin D are more likely to lose their balance and fall, possibly because of vitamin D's role in promoting muscle function [1]. Higher blood levels of vitamin D have been associated with a lower risk of having colon cancer [2] and a decreased risk of dying from colorectal cancer [3].

In addition, lower rates of type 2 diabetes [2], hypertension [4], multiple sclerosis [5], and depression [6] have also been reported in people with higher blood levels of vitamin D.

Where Do We Get Vitamin D?

Vitamin D comes from two places - we take it into our bodies in foods and supplements, and our bodies produce it after sunlight exposure. Vitamin D is found naturally in only a few foods like fatty fish (for example, cod liver oil) and egg yolks. Because there are so few natural dietary sources, vitamin D is added to foods such as fortified soymilk, fortified juice, fortified breakfast cereals, cow's milk, and margarine. (Vegan spreads like Earth Balance do not have vitamin D added.) Typically, soymilk is fortified with vitamin D2, the vegan form of vitamin D, while cereals, juice, and margarine are fortified with vitamin D3 that is usually derived from sheep's wool. If the label on a fortified food doesn't say what form of vitamin D is used to fortify the food, you can contact the company.

Mushrooms that are commercially exposed to ultraviolet B light have relatively high levels of vitamin D, close to 1,000 International Units (IU) in a 1-cup serving [7].

Besides vitamin D from food and supplements, our bodies are able to make vitamin D when our skin is exposed to ultraviolet B rays from sunlight under certain conditions. It doesn't take much sun to stimulate vitamin D production, just 15 minutes a day on hands, arms, and face. [8] However, this sunlight exposure only works at certain times of day and in certain seasons above certain latitudes (or below certain latitudes if you're in the Southern Hemisphere). Vitamin D production is highest when the sun's rays are most intense - between 10 a.m. and 3 p.m. during the summer months. In locations above 42 degrees north latitude (Chicago, Boston, and Portland, Oregon, for instance), vitamin D production does not occur from late October through early March. Even as far south as Atlanta (about 35 degrees north latitude), vitamin D production doesn't occur from November to February [9].

Factors like sunscreen use, darker skin pigmentation, clothing, pollution, and aging can reduce the amount of vitamin D we produce. Because of this and because of concerns about sun exposure leading to skin cancer, many people feel safer relying primarily on foods or supplements for vitamin D.

How Much Vitamin D Do We Need?

The current recommendation for vitamin D is 400 IU per day for infants from birth to 1 year; 600 IU per day for children and adults up to 71 years old, and 800 IU per day for those age 71 years and older [10].

Can We Get Too Much Vitamin D from Food or from Supplements? Will Our Bodies Make Too Much Vitamin D?

It is possible to get too much vitamin D, by overdoing supplements. Excess vitamin D can cause the body to absorb too much calcium and can lead to kidney damage. Long-term use of vitamin D supplements providing more than the Upper Limit set by the Institute of Medicine can increase the risk of adverse health effects. The Upper Limit for vitamin D is 2,500 IU/day for 1-3 year olds, 3,000 IU/day for 4-8 year olds, and 4,000 IU/day for those 9 years and older [10].

Don't worry about producing too much vitamin D following sun exposure because your skin stops producing it once you've had enough. It's still a good idea to limit sun exposure, however, because of the link between sun exposure and skin cancer.

Is Vitamin D a Special Concern for Vegans?

It is difficult to plan a vegan diet, or any type of vegetarian diet, that meets the recommendations for vitamin D. For example, you'd need to drink 4 or more cups of vitamin D-fortified plant milks or of fortified dairy milk to meet vitamin D recommendations. Any person, whether vegan or not, who does not include good sources of vitamin D in his or her diet or take vitamin D supplements can be at risk for not getting adequate vitamin D, especially if sunlight exposure is limited. Some studies have found that vegans had lower vitamin D intakes [11] and lower blood levels of vitamin D [12] than did lacto-ovo vegetarians or meat-eaters. This may be because cow's milk (a source of vitamin D due to fortification) could be a more common part of the daily menu for non-vegans than other vitamin D-fortified foods are for vegans.

What Happens If Someone Doesn't Get Enough Vitamin D?

A vitamin D deficiency leads to nutritional rickets, a condition that causes weak and deformed bones in babies and children. Symptoms can include a delay in learning to walk, low height-for-age, and bowing of the legs and arms. Rickets rarely occurs in the U.S., but a recent outbreak of cases has raised concerns that children are not getting enough vitamin D.

In adults, not getting enough vitamin D can increase risk of osteoporosis and other diseases.

What's The Difference Between Vitamin D2 and Vitamin D3?

Two different forms of vitamin D are used in supplements and fortified foods. Vitamin D2, also called ergocalciferol, is manufactured through the ultraviolet irradiation of a substance called ergosterol that comes from yeast. Vitamin D2 is vegan.

Vitamin D3, also called cholecalciferol, is typically made by the ultraviolet irradiation of a substance derived from sheep's wool. A plant-sourced vitamin D3 has been discovered and is being used in vegan supplements.

Both vitamin D2 and vitamin D3 appear to be effective in preventing vitamin D deficiency [13], but high doses of vitamin D3 may be more potent [14]. If you are treated for a vitamin D deficiency, you may find that your health care provider recommends taking a higher dose of vitamin D2 than of vitamin D3 to compensate for possible differences in potency [9].

What About Vitamin D For Breast-fed Babies?

Breast milk is the ideal food for infants. Human milk, however, contains little vitamin D. If a nursing mother is vitamin D-deficient, her breast milk will be even lower in vitamin D than usual. To prevent vitamin D deficiency in breast-fed babies, the American Academy of Pediatrics recommends that breast-fed babies be given a 400 IU/day vitamin D supplement beginning within the first few days after birth [15].

One study found that lactating women who took a vitamin D supplement containing 6,400 IU of vitamin D3 had breast milk that contained enough vitamin D to meet their infants' needs [16]. This could be an alternative to giving the infant a vitamin D supplement. While there is some possibility that a baby will be able to make adequate vitamin D following sunlight exposure, there are many factors that interfere with vitamin D production (skin pigmentation, pollution, season, amount of clothing, location, and sunscreen). This is why supplemental vitamin D is recommended.

Vitamin D Sources for Vegans

• Vegan Vitamin D3 Now Available in the US 

• Vitashine Vegan Vitamin D3 Supplements 

• Vitashine Vegan D3 information

Reed Mangels, PhD, RD, is one of The Vegetarian Resource Group's Nutrition Advisors. She is the co-author of Simply Vegan and has written many articles for dietetic and health journals.

References