Vitamin D: deficiency, food sources and what you need to know

(CNN) – You may have seen supplements with vitamin D in your local neighborhood stores or have been tested for a deficiency by your doctor. But what is vitamin D and why do we need it?

The nutrient plays a major role in bone maintenance by helping us absorb calcium. Our bodies naturally produce it when we are exposed to sunlight, and some foods that we eat can naturally contain or be enriched with it. All vertebrates, not just humans, need vitamin D.

Too little vitamin D can lead to a deficiency, which is associated with the development of softening and weakening bones. These symptoms manifest themselves as rickets in children and osteomalacia in adults.

Vitamin D sources

Vitamin D is found in various foods that we eat. Fatty fish, such as tuna, salmon, cod and mackerel, all contain high levels. Other foods, such as milk and orange juice, can be strengthened with it. There are also self-care additions that you can take; however, some contain well the recommended daily amount and research has questioned their effectiveness. But the easiest way to get vitamin D is to just go outside on a sunny day.

A type of cholesterol that is present through the skin naturally absorbs UVB radiation from the sun and converts it into a form of vitamin D.

Dr. Clifford Rosen, professor of medicine at the Tufts University School of Medicine and senior scientist at Maine Medical Center, said it is generally better to extract vitamin D from the sun and food than from supplements.

Besides the fact that the sun is free while bottles of supplements are not, it is possible to take too much vitamin D, which could increase the risk of kidney stones and other health problems, Rosen said. The patients he sees who usually have an excess of vitamin D take daily supplements with 5000 to 10,000 units of the vitamin, considerably more than the recommended daily amount.

On the other hand, biochemical pathways in our body prevent us from producing too much vitamin D as a result of sun exposure, so it is not possible to take an overdose like that, said Paul Thomas, a scientific adviser to the Office. or Dietary Supplements from the National Institutes of Health. .

Vitamin D benefits

In addition to keeping bones strong by helping the body to absorb calcium, vitamin D has been associated with a reduced risk of a number of conditions, such as osteoporosis, hypertension and cancer. Other research suggests, however, that vitamin D supplements can not be a panacea.

Thomas said it is safe to assume that the benefits of vitamin D are marginal at best, although researchers are not sure until large, randomized studies have been conducted and the results analyzed.

"For many of the nutrients that maintain health or treat diseases, the effect will be very small at best," he said.

Another problem in studies that associate low vitamin D levels with disease is a lack of causality, Rosen said. Sick people can have a lower vitamin D content due to their disease, not necessarily the other way around.

How much vitamin D is enough?

In 2010, a committee of the Institute of Medicine, now known as the National Academy of Medicine, recommended new guidelines for vitamin D intake and adequate blood serum levels of a vitamin D biomarker. Rosen, who served in the committee, said that people usually run the risk of developing a deficit if their serum level of the biomarker is lower than 12 nanograms per milliliter, far below the adequate level of 20 ng / ml.

It is counterproductive to talk about inadequacy or inadequacy of vitamin D, because these levels are often relative, Rosen said, and can lead to conclusions that the majority of the US population is inadequate or a small minority, depending on the value chosen. "inadequate".

To reach the 20 ng / ml blood serum level of the vitamin D biomarker, the National Institutes of Health recommends an average daily amount ranging from 400 to 800 international units of the vitamin, depending on a person's age.

Thomas said there is "a range where you can play," from the middle hundreds to about 4,000 units of the vitamin a day, the safe upper limit according to the National Academy of Medicine.

Vitamin D deficiency

Symptoms of vitamin D deficiency may include bone and muscle weakness, increasing the risk of fractures and falls for older adults. In children, a deficiency can lead to a softening of the bones known as rickets. After scientists discovered the link of rickets with vitamin D deficiency in the 1900s, they started enriching foods with the vitamin, and the disease is now considered a rare disease by the National Institutes of Health.

For most people, vitamin D deficiency does not develop out of the blue, Thomas said. People who seldom go out or are extremely picky eaters may be in danger, but for the majority of people what they do is fine, he added.

Nevertheless, Rosen said that 10% or more of the people who come in for routine controls are tested for vitamin D deficiency, which is completely unnecessary if they show no symptoms, he said.

"Doctors want to measure something," he said, adding that finding a serum level under the adequacy and prescription of a pill is a quick solution that can make the doctor successful. "If we did not have supplements, I do not think we would measure vitamin D."

The CNN-Wire
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