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Study: Low Vitamin D Not a Cause of Disease

December 6, 2013

News Review From Harvard Medical School — Study: Low Vitamin D Not a Cause of Disease

Some studies have found low vitamin D levels among people with illnesses such as cancer, diabetes and heart disease. But a new review of medical evidence says it’s unlikely that low vitamin D caused the diseases. Researchers looked at almost 500 studies. They fell into 2 main types. The observational studies took a look at people who had high or low levels of vitamin D in their bodies. They found higher rates of heart disease, cancer, diabetes and other diseases among people with low vitamin D. The other type of study compared people who were randomly assigned to receive vitamin D pills or placebo (fake) pills. These studies did not find any health effects for the people who received the real vitamin D pills. The only exception was for older adults, especially women. Those who took vitamin D were less likely to die during the studies. Researchers said that was likely because of fewer fractures. Vitamin D helps to strengthen bones. The difference between these 2 types of studies suggests that the diseases led to low vitamin D, not the reverse, researchers said. The journal Lancet Diabetes & Endocrinology published the study online. HealthDay News wrote about it December 5.

By Mary Pickett, M.D.
Harvard Medical School

What Is the Doctor’s Reaction?

My medical practice is in Oregon. Oregon is a lovely place, but the sky here is frequently rainy and gray. My patients here joke, “In Oregon, we don’t tan, we rust.”

My patients don’t get much vitamin D from sun exposure. Many doctors here feel that living in Oregon is enough reason in itself to check a vitamin D level on every patient from time to time. Out here, more than most places, it is trendy for people to take vitamin D pills. Across the United States, half of adults take vitamin D. Americans spend about $600 million per year on these supplements.

So how important is this vitamin? Vitamin D seems to be low among people with a lot of diseases. I have seen true believers who think low D will lead to cancer, heart attacks, Parkinson’s disease, infection or even early death.

But is this true? A new review of the evidence as much as says, “Stop the hype!” The report, released this week by the journal Lancet, makes a convincing case that as far as it relates to these health problems, low vitamin D is a result of having chronic disease, not a cause of these illnesses.

Vitamin D does have a few important proven benefits. These benefits relate to bone and muscle health.

  • Children low in vitamin D can develop “rickets,” a bone growth problem.
  • Adults who have falls are less likely to have repeated falls if their vitamin D level is brought up with supplements.
  • Low vitamin D can lead to osteoporosis (thin bones). Vitamin D helps you to pack calcium into your bones to strengthen them.

Is there harm to taking vitamin D pills if you don’t need them? Not much, if you take the usual doses. The exception is a small increased risk of kidney stones. At very high doses, vitamin D can create a build-up of calcium in your blood. This can cause belly pain, kidney stones, hardening of your arteries and nausea.

One group that takes a lot of vitamin D is women who have passed menopause. They are taking vitamin D because of a desire to prevent osteoporosis. This February, the U.S. Preventative Services Task Force published new advice, telling women after menopause not to take calcium pills with vitamin D, unless they already have:

  • Osteoporosis
  • A history of fracture
  • A problem with falls

Even low daily doses — 400 international units of vitamin D along with 1,000 milligrams of calcium — increase the risk of kidney stones.

What Changes Can I Make Now?

Not everyone needs to have a vitamin D level checked, and not everyone needs to take vitamin D pills.

I recommend that you have your vitamin D level checked if you have:

  • Very limited sun exposure
  • Bowel disease or bowel surgery that has led to limited nutrition
  • Repeated falls, muscle pain or weakness
  • Severe obesity (this increases the risk of low vitamin D)
  • Low bone density on a bone density test (osteopenia or osteoporosis)

If you are in one of these groups and your blood test shows a vitamin D level of less than 20 nanograms per milliliter (ng/mL), you should definitely take a supplement. Traditionally, doctors start with a high dose. Then we change to over-the-counter doses after the level is brought up to normal.

What if you are not in these groups? It is probably enough for you to get out into the sunshine and to drink your milk.

What Can I Expect Looking to the Future?

Several large studies now underway will compare vitamin D to placebo pills. The goal is to find out if there is a genuine protective effect from vitamin D against a variety of diseases. For example, a study known as VITAL is enrolling 20,000 people. They will be randomly assigned to take or not take vitamin D pills. Researchers will look at the rates of heart disease, cancer and stroke that occur over time in both groups.

This study and others like it mean we will eventually have more definite knowledge about vitamin D. We will better understand whether vitamin D has health benefits beyond its effects on bones and muscles. I am not expecting to see a strong positive result from these studies, however. If I had that much faith in vitamin D, I might not have chosen to live in beautiful Oregon.


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