How much vitamin D should you take?

  • Too much vitamin D can result in reduced bone density.
  • The best sources of vitamin D are fatty fish and fortified dairy products. 
  • Your body produces vitamin D after sun exposure.

Vitamin D has been proven to help strengthen the bones. However, a recent JAMA study has found that taking large amounts of vitamin D may reduce bone density. 

Studies on high-dose vitamin D

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In the said JAMA study, 300 healthy adults were given daily doses of 400 international units (IU), 4,000 IU, or 10,000 IU of vitamin D supplements. When the study began, all participants had their bone mineral density tested to assess their bone health, then took the supplements for three years.

Note that the recommended daily intake of vitamin D for adults through age 70 is 600IU, and 800 IU for people above age 70. This means the amount given to the participants are well beyond what is recommended, says Dr. JoAnn E. Manson of Harvard Medical School. However, the study found no significant improvement in bone density among the participants. 

Too much of a good thing

According to national survey data gathered from 1999 to 2014, a 2.8% increase was found in the number of people taking more than 4,1000 IU of vitamin per day. Further, an 18% increase in the number of people taking 1,000 IU or more of vitamin D daily was also found. 

According to Dr. Manson, only those with Crohn’s disease, ulcerative colitis, and people who have had gastric bypass surgery need higher amounts of vitamin D supplements. 

The potential effects of vitamin D supplementation

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Dr. Manson heads a large ongoing study on how vitamin D and omega-3 supplements lower risks for cancer, cardiovascular disease, and other conditions. She explains that while there is scientific data to support vitamin D’s role in bone health and reducing cancer-related deaths, there is no conclusive evidence that it prevents conditions unrelated to bone health. 

According to two meta-analyses published by Dr. Manson and her team, vitamin D seems to help lessen the risk of death from cancer but doesn’t seem to prevent cancer itself. This may imply that vitamin D could make tumors more manageable. However, Dr. Manson and her team also found that vitamin D supplements do not prevent heart attack or stroke. 

Studies are still ongoing on whether vitamin D plays a role in protecting cognitive function and preventing infections, depression, and diabetes.  

Tips for supplementing on vitamin D

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Stick to moderate amounts. Dr. Manson says you can take 1,000 IU of vitamin D a day if you’re concerned about getting enough. Natural sources include fatty fish and fortified dairy products. Your body also produces vitamin D after sun exposure. However, people over age 65 produce lesser vitamin D than 25-year-olds. 

Consult your doctor. Taking large doses of vitamin D should be done under the advice of your health care provider.

Vitamin D overdose may lead to hypercalcemia, which occurs when too much calcium builds up in the blood and results in deposits forming in the arteries or soft tissues. It may also increase your risk of kidney stones. 

Choose natural sources. As much as possible, get your vitamin D from food sources instead of supplements. 

Sources: Harvard Health Publishing

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