Taking too much vitamin D can mask its benefits and create risks - Harvard

Vitamin D supplements are growing in popularity, but they are not always needed and taken in the right doses.

Taking too much vitamin D can affect its effectiveness and create risks

Some people go overboard in their pursuit of better health.

Vitamin D is having its day in the sun.In recent years, studies have linked low blood levels of the vitamin to an increased risk of heart disease, diabetes and cancer, as well as mood disorders and dementia.The findings did not go unnoticed.Vitamin D supplements and screenings are becoming more popular.

"The test for vitamin D is one of the best clinical laboratory tests conducted in the United States in recent years," says Dr. Joanne E., Michael and Lee Bell Professor of Women at Harvard Medical School.Manson." That's pretty surprising for a test that's only recommended for a small subset of the population."

Unfortunately, this vitamin D trend is not only blue sky: some people are overusing the supplement.Researchers studying national survey data collected between 1999 and 2014 found a 2.8% increase in the number of people taking potentially unsafe doses of vitamin D, which is more than 4,000 international units (IU) per day, according to research published in the June 20 issue of the Journal of the American Medical Association (JAMA) and around the same time. The number of people taking 1,000 IU or more ofVitamin D per day increased by nearly 18%, exceeding the recommended amount of 600 to 800 IU for most people.

Vitamin D and yours

Vitamin D, known as the "sunshine vitamin" because your body produces it after exposure to the sun, has long been known to help build strong bones by increasing the body's absorption of calcium and phosphorus.But starting in 2000, research into the role of vitamin D in other conditions began to expand rapidly.

Dr. Manson says that while there is strong support for vitamin D's role in bone, the evidence that it prevents other conditions is not yet clear."Research on vitamin D and calcium supplements has been mixed, and especially when it comes to randomized clinical trials, they've been generally disappointing to date," he said.

Manson is the principal investigator of the recently announced Vitamin D and Omega-3 Trial (VITAL), a large study (more than 25,000 participants worldwide). The study found that people taking vitamin D supplements did not reduce their risk of heart attack, stroke, or cancer.However, among those who later developed cancer, those who took vitamin D supplements for at least two years had a 25% lower cancer death rate compared with those who received a placebo.

Factors Affecting Your Vitamin D Levels Your vitamin D levels reflect many factors.For example: where you live.If you live in northern states (north of 37 latitude), you are at a higher risk of vitamin D deficiency because your skin cannot produce vitamin D due to sun exposure during the winter months.your age.Your skin's ability to produce vitamin D decreases with age.If you're over 65, you produce only one-fourth as much vitamin D as you did in your 20s.Your skin color.People with darker skin generally have lower levels of vitamin D than people with lighter skin.African Americans generally have more vitamin D in their blood than white Americans.Used by the body.The food you eat.Very few foods naturally contain vitamin D. The US government began a program to fortify milk with vitamin D in the 1930s to combat rickets, a bone-weakening disease caused by vitamin D deficiency, which was a major public problem at the time.Breakfast cereals and some orange juices can be fortified, but this varies by type.Therefore, the amount of vitamin D you get from food depends on the foods you eat and the amount of milk you drink.Some conditions.People with conditions such as tuberculosis, liver disease, or cystic fibrosis may have problems absorbing vitamin D, which can lead to a deficiency.|

Looking for the link

Although some studies have found a link between low levels of vitamin D in the blood and various diseases, it has not been conclusively proven that vitamin D deficiency causes disease, says Dr Manson.

For example, a seriously ill person may have a vitamin D deficiency.However, this could be because he or she spends little time outdoors for physical activity, or because the person has a poor diet — both of which are risk factors for many diseases and can also cause deficiencies, says Dr. Manson. Another problem is that illness can cause inflammation, which can lower vitamin D levels in the blood.Obesity, which is associated with many medical conditions, can reduce the amount of vitamin D in the blood because your body stores the vitamin in fat tissue and removes it from the bloodstream, where it will show up in tests.

In addition to finding out whether vitamin D deficiency causes disease, more studies are needed to determine whether taking supplements can reduce these risks, Dr. Manson said.

Vitamin D benefits and warnings

Although the research is not clear, some people will benefit from taking vitamin D supplements, along with adequate calcium intake, to promote their bone health.But they don't need large amounts of vitamin D to benefit."More is not better. In fact, more can be worse," said Dr. Manson.For example, a 2010 study published in JAMA showed that high intakes of vitamin D in older women were associated with more falls and fractures.

Also, taking a supplement that contains too much vitamin D can, in rare cases, be dangerous.This can lead to hypercalcemia, a condition in which too much calcium builds up in the blood, which can form deposits in the arteries or soft tissues.It can also cause kidney pain in people.

If you take vitamin D supplements, the take-home message is moderate.Consuming too much can limit the benefits of the sunscreen.

Selected food sources of vitamin D |

International units |

Salmon, pink, cooked, 3 ounces |

Tuna, canned in oil, drained, 3 oz |

Sardines, canned in oil, drained, 3 ounces |

Milk, nonfat, fortified, 8 oz

Orange Juice, Fortified, 8 oz |

Egg, whole, hard-boiled, cracked, 1 large |

Cheddar cheese, 1 oz.

Frozen Yogurt, Flavor Other Than Chocolate, 8 Ounce |

Source: USDA National Food Data for Standard Reference.|

Be smart about D

To take vitamin D supplements safely, it is best to follow some simple rules;

Pay attention to your numbers.If you take a vitamin D supplement, you don't need more than 600 to 800 IU per day, which is enough for most people.According to Dr.Manson, some people may need a higher dose, including those with arthritis and those with vitamin D or calcium absorption problems.

Choose food over pills.If possible, get vitamin D from food sources rather than supplements (see "Selected food sources of vitamin D").Choose fortified dairy products (where nutrients have been added to the food), fatty fish and dried mushrooms.D Food content.

Let your doctor know. "Many people overdose on supplements themselves and even their doctors don't realize it," says Dr. Manson. Discuss supplement use with your doctor to make sure you're taking the right amount for your needs. If you regularly eat a balanced diet that includes good sources of vitamin D, you may not need a supplement.

As a service to our readers, Harvard Publishing provides access to our archived content library.Please remember the date all articles were last revised or updated.

No content on this site, regardless of date, should be used as a substitute for direct medical advice from your physician or other qualified clinician.