Vitamin D holds promise for many things, like building bone, preventing heart attacks and strokes, reducing cancer risk, and more. But that promise isn’t fully backed by science. For example, a controlled clinical trial published this week in JAMA Internal Medicine found that a vitamin D supplements didn’t build bone in postmenopausal women with blood levels of vitamin D below the threshold generally considered necessary for good health. Many researchers are looking ahead to results from an ongoing trial called VITAL, which aims to gather the kind of solid evidence that will let us know for sure whether taking relatively high doses of vitamin D can ward off heart attack, stroke, or cancer. The results are expected by the end of 2017. It’s also possible to get vitamin D the old-fashioned way: go out in the sun between 10 a.m. and 3 p.m. with at least 10% of your skin exposed. Stay out long enough to absorb the sun but not long enough to be burned.
Nearly 2 billion people around the world are anemic, meaning they don’t get enough iron to produce the red blood cells and oxygen-carrying hemoglobin needed to nourish their myriad cells. In developed nations like the United States, though, iron-poor blood is uncommon. The body stores most of its iron in hemoglobin inside red blood cells and in ferritin, a protein that latches onto iron and sequesters it in the liver, spleen, and bone marrow. Most Americans get all the iron they need from food. The body absorbs iron from meat more easily than it absorbs it from plants. Getting enough vitamin C helps the body absorb iron from food. Because the body does not excrete iron rapidly, it can build up over time and possibly cause problems. That’s why it’s a good idea to ask your doctor if you need to take an iron supplement.
What harm can having too little of a vitamin do? Consider this: Over the course of two months, a 62-year-old man developed numbness and a “pins and needles” sensation in his hands, had trouble walking, experienced severe joint pain, began turning yellow, and became progressively short of breath. The cause was lack of vitamin B12 in his bloodstream, according to a case report from Harvard-affiliated Massachusetts General Hospital published in The New England Journal of Medicine. It could have been worse—a severe vitamin B12 deficiency can lead to deep depression, paranoia and delusions, memory loss, incontinence, loss of taste and smell, and more, according to another article in tomorrow’s New England Journal. Some people, like strict vegetarians, don’t take in enough vitamin B12 every days. Others, like many older people and those who have had weight-loss surgery or live with celiac disease or other digestive condition don’t absorb enough of the vitamin. Daily supplements can help.