Vitamin D is a popular topic. Studies about vitamin D supplements often appear in the news media. It is important for consumers to keep in mind what we know, and what we don’t know, about this fat-soluble nutrient.
Virtually all cells in all tissues in the bodies express the vitamin D receptor protein that allows the body to respond to vitamin D. For bone health, vitamin D allows calcium and phosphorus to be absorbed in the intestines. Vitamin D enables bones to be formed in childhood and remodeled throughout the lifespan.
Children who don’t have enough vitamin D can develop rickets, a condition marked by soft bones, weakened muscles, and deformed joints. Adults who are deficient in vitamin D can develop a similar condition called osteomalacia. Having enough vitamin D is also important for preventing osteoporosis and reducing fracture risk.
Although vitamin D can be made in the skin when it is exposed to sunshine, the sun is not a reliable source of vitamin D for most people. Use of sunscreen blocks the vitamin D benefits of exposure to sunshine. Prolonged exposure to sunlight also is a risk factor for skin cancer.
It is challenging to get enough vitamin D in your diet. There are a few food sources of vitamin D, such as fatty fish (salmon, mackerel and sardines), mushrooms exposed to UV light, fortified cereals, juices, and egg yolks. If you do not get enough vitamin D through sun exposure and diet, your health care provider may suggest that you take a supplement to get enough vitamin D. Remember to check the amount of Vitamin D in any multivitamin or calcium supplement you are taking.
A blood test measuring 25-hydroxyvitamin D3 can tell whether you have enough vitamin D. There are differing opinions on what is the best level for bone health. The Endocrine Society considers a level at or above 30 ng/ml to be “sufficient.” Some guidelines consider a level below 20 ng/ml to be “deficient.” Vitamin D insufficiency or deficiency is common in the United States. The U.S. recommended daily allowance for a supplement of vitamin D is 600 IU; for adults who are pregnant or nursing or older than 70, the recommendation is 800 IU. Your health care provider might prescribe a higher dose to try to increase your 25-hydroxyvitamin D level.
So, we know that having enough vitamin D is an important factor for bone health and general health. We know that people who don’t have enough vitamin D are at higher risk of developing osteoporosis and having falls and broken bones. We know that taking a supplement can boost your vitamin D levels.
What we don’t know is whether taking supplements can reduce risk of fractures in healthy people who have enough vitamin D. In 2022, a study done in support of the Vitamin D and Omega-3 Trial (VITAL) found that taking a vitamin D supplement “did not result in a significantly lower risk of fractures than placebo among generally healthy midlife and older adults.”
Medical societies like the Endocrine Society do not recommend regular vitamin D screening for healthy people. Some physicians do recommend supplements for people who are low on vitamin D or have certain medical conditions that may or may not be related to bone health.
Bottom line: Having enough vitamin D is necessary for good bone health. Having more than enough isn’t necessarily better for your bones.
