With so much focus on vitamin D deficiency, it’s easy to forget that you can get too much of the “sunshine” vitamin. You won’t get too much from sun exposure since your body has mechanisms for regulating vitamin D you get from sunlight. UVB rays from the sun are the best source of vitamin D for most people as most foods don’t contain substantial quantities of vitamin D. The foods that contain vitamin D are fatty fish, egg yolks, and beef liver. Plus, some foods, like milk and breakfast cereal, are fortified with vitamin D.
Because of foods being deficient in vitamin D and a lack of sun exposure, more people are taking a vitamin D supplement. Some people need extra vitamin D, but too much vitamin D can be risky. Too much of a good thing isn’t always better!
The Risks of Too Much Vitamin D
Vitamin D is a vitamin your body stores when you consume it through food or supplements. The place it stores excess vitamin D is in fat cells. When your body needs more vitamin D, the liver and kidneys activate the stored vitamin D so your body can use it. If you are overweight or obese and have lots of stored fat, you have more room to store vitamin D. But what if you have little body fat? If that’s the case, you have fewer fat cells to store vitamin D so more stays in the bloodstream and is available to tissues. Beyond a certain point, that could be harmful.
You need a certain amount of vitamin D for healthy bone metabolism. If you were very low in vitamin D, you could develop a vitamin D deficiency disease called osteomalacia. Osteomalacia is the adult form of a vitamin D deficiency disease called rickets. Kids with rickets have soft bones that cause deformities, like bowed legs and an abnormally curved spine. Children with rickets can have other problems too, including slow growth and bone pain. Adults with osteomalacia have poor mineralization of bones and are at risk of bone pain and fractures.
Beyond bone health, studies are looking at whether maintaining a high enough level of vitamin D is important for preventing other health problems such as cardiovascular disease or cancer. Thus far, studies are conflicting as to whether supplementing with vitamin D to raise levels lowers the risk of chronic health problems. However, there is evidence that people with some autoimmune diseases, like multiple sclerosis, benefit from maintaining a higher vitamin D level. One study found that a vitamin D level of less than or equal to 30 ng/ml was linked with higher mortality. This level is higher than what most physicians consider adequate, greater than 20 ng/ml.
Why You Shouldn’t Overdo the Vitamin D Supplements
Since we know that our bodies store excess vitamin D, excessive amounts are undesirable, as your body can’t eliminate the excess. Studies show that taking high doses of vitamin D as a supplement can increase the amount of calcium that enters the urine. This, in turn, increases the risk of kidney stones. The risk is higher in people who take vitamin D and calcium in supplement form. It’s not clear whether the calcium is contributing more to the calcium in the urine or whether it’s the combination of calcium and vitamin D. Taking very large doses of vitamin D can also increase the amount of calcium in your blood and cause digestive symptoms such as nausea, vomiting, and increased urination.
Some studies suggest that vitamin D supplements may lower the risk of upper respiratory infections. However, taking high doses, over 2,000 I.U. daily, is correlated with a higher risk of developing upper respiratory infections compared to taking a low dose, around 400 I.U. daily. Also, a study in multiple sclerosis patients who took a high-dose vitamin D supplement daily showed that vitamin D decreased release of melatonin, a hormone that controls the onset of sleep and the body’s internal biological clock. So, taking too much vitamin D could negatively impact sleep quality.
Should You Check Your Vitamin D Level?
One of the best ways to avoid taking too much vitamin D and ensure you’re getting enough is to check your vitamin D level. Doctors still don’t recommend routine vitamin D testing for everyone but suggest that people at risk for deficiency consider getting a level checked. It’s not wise to take high doses of vitamin D without testing your level first. Who’s at risk of deficiency?
- Being over the age of 65. Vitamin D production drops with age.
- Living in Northern parts of the United States or having little sun exposure.
- Having a body mass index greater than 30.
- Having darker skin pigmentation.
- Having health conditions that reduce vitamin D absorption, including inflammatory bowel disease, cystic fibrosis, and liver disease.
One study also found that most people who have had a heart attack are low in vitamin D.
The Bottom Line
More isn’t always better when it comes to vitamins, especially if you’re getting them in supplement form. If you don’t know your vitamin D level, don’t take more than 1,000 to 2,000 I.U. of vitamin D daily. This amount is safe for the average person. However, it’s best to check with your physician before taking supplements, including vitamin D since some can interact with medications and with each other. Excessive amounts of vitamin D can be harmful and there’s little evidence that taking high supplemental doses offers benefits. If possible, get your vitamin D from daily sun exposure. Your body has mechanisms for regulating the vitamin D you get from sunlight. But make sure your vitamin D doesn’t drop to low. Ask your physician whether they recommend vitamin D testing.
References:
- Endocr Connect. 2019 Feb; 8(2): R27–R43.Published online 2019 Jan 16. doi: 10.1530/EC-18-0432.
- Mayo Clinic. “What is vitamin D toxicity, and should I worry about it since I take supplements?”
- Brain Behav Immun. 2013 Aug;32:180-5. doi: 10.1016/j.bbi.2013.04.010. Epub 2013 May 7.
- Am J Cardiol. 2011 Jun 1;107(11):1636-8. doi: 10.1016/j.amjcard.2011.01.048. Epub 2011 Mar 23.
- Am J Public Health. 2014 August; 104(8): e43–e50.
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