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Can you over-do vitamin D?

Check your supplements — more isn’t always better

By Jan Adams-Kaplan, RD, CDE

Woman taking vitamins

For Portlanders, moderate deficiency in “the sunshine vitamin” is about as common as a cloudy day. Since we can’t get the daily sun exposure needed to synthesize our own vitamin D year-round, many of us pop a supplement to keep our levels in check — and in most cases, that’s a good thing. But in some cases, we could be taking too much — and that can be a problem.

You need vitamin D to help you absorb calcium, among other benefits. But extra high blood levels of vitamin D may encourage your body to stash extra calcium where it’s not wanted — in your kidneys, for example, which is why high levels of vitamin D make you more vulnerable to kidney stones. Calcium deposits in the arteries are another potential concern. High vitamin D levels also can cause nausea, vomiting, muscle weakness, confusion, loss of appetite, dehydration and frequent urination.

When people have too much vitamin D in their blood, it’s almost always caused by over-use of dietary supplements. That doesn’t mean you should stop taking vitamin D altogether, but do take a closer look at how much you’re taking to make sure you’re not overdoing it.

Enough vs. too much — where do you draw the line?

The recommendations may vary depending on your age, health, ethnicity — and even whom you ask. But as a general guideline, the National Institutes of Health Office of Dietary Supplements (ODS) recommends getting 15 mcg (600 IU) of vitamin D daily from the age of 1 through 70, and 20 mcg (800 IU) from age 71 on.

In Portland’s darker days, taking a little bit more than that won’t hurt, but keep an eye on it. The upper tolerable limit, as set by the Institutes of Medicine, is 4,000 IU per day. It’s very easy to accidentally take more than that, and a growing number of Americans do.

Two ways we get into trouble

Taking multiple supplements: if you take a multivitamin, a calcium supplement and a vitamin D supplement, you could be getting much more vitamin D than you realize. A recent survey of one patient’s medicine cabinet turned up the following:

  • A multivitamin with 1,000 IU of vitamin D
  • A calcium supplement with 1,600 IU of vitamin D (for “one serving,” which provided only half of the daily recommended calcium; a full day’s calcium would deliver 3,200 IU of D)
  • Two vitamin D supplements ranging from 1,000 to 5,000 IU

For this person, the daily intake of vitamin D from all sources could range from 3,600 to 9,200 IU, depending on which D supplement she grabbed and how much calcium she took.

The totals from all sources can add up quickly. To stay out of trouble, check all of your supplements and do the math; the amounts of vitamin D per serving are listed on the back of the bottle, right under “Supplement Facts.”

Taking high-dose vitamin D for too long: high-dose vitamin D — such as 50,000 IU per week — is sometimes prescribed to correct blood levels that show severe deficiencies. These therapeutic dosages are meant to be temporary, not long term, but sometimes people lose track and keep taking them long after they’ve done their job.

If you’ve been prescribed high-dose vitamin D, work closely with your doctor to monitor your blood levels. It can take three months or more to bring them back up, but once they’re good, you can stop the high doses and return to a lower vitamin D supplement for maintenance.

Should everyone have their vitamin D level tested?

Even though moderate vitamin D deficiency is common in our part of the world, that doesn’t mean we all need to be tested for it. Serious deficiencies are still relatively uncommon.

That said, certain people are at higher risk. This group includes:

  • Older adults
  • People with dark skin
  • People who have osteoporosis
  • People who are obese or have had gastric bypass surgery
  • People with digestive diseases that limit their ability to use vitamin D, such as celiac disease, inflammatory bowel disease, and diseases of the liver, pancreas and kidneys
  • Vegetarians and vegans

If you’re in a higher-risk group, your doctor can help you determine whether a vitamin D test makes sense for you. (Some insurers don’t cover vitamin D testing for everyone. Home testing may be coming down the line, but we’re not there yet.)

For many of us, a blood test probably won’t change our health care provider’s advice. If you are found to have a slight vitamin D deficiency, the usual recommendation is to pay more attention to getting D from food sources like fortified milk, fatty fish and mushrooms (tip: look for mushrooms that have been exposed to light — they need light to synthesize D just like we do), and to take a supplement (but not too much). These are all things that we Portlanders should be doing anyway.

Learn more from the Office of Dietary Supplements’ vitamin D fact sheet.