Over time, the extra calcium can form deposits in the arteries and soft tissue instead of in the bones. Ultimately, this can cause kidney stones and may contribute to heart damage.
"This is the major impact of acute vitamin D toxicity, and it may be occurring slowly in people taking high vitamin D for years," says Paul Price, Distinguished Professor Emeritus of Molecular Biology at University of California San Diego.
To diagnose vitamin D toxicity, a physician will administer a blood test that will show how much calcium is in the blood. If a person has vitamin D toxicity, then calcium levels will be abnormally high.
Ross notes that taking consistently high levels of vitamin D over long periods of time may not cause apparent toxicity in the short-term, but may contribute to higher risk of common symptoms further down the line.
The National Institutes of Health recommend that most adults need 600 international units (IU) each day to cover their basic needs for bone health. However, for overall health, it's best to get somewhere between 600 IU to 4,000 IU per day.
Fish is a great way to cover your bases, while vegans and vegetarians can look to almond milk and mushrooms. Three ounces of fatty fish, like salmon, or a cup of portobello mushrooms will take care of your daily vitamin D needs.
Ross says that if you occasionally consume the maximum recommended amount — 4,000 IU — it won't hurt you. But if you are consistently reaching or exceeding this limit for months or years on-end, that's when it may lead to symptoms of toxicity.
Vitamin D research has received a lot of attention in recent years, and many potential benefits are emerging. Supplements are not necessarily off the table, but don't go in thinking more is better — unless you love kidney stones.
Too much vitamin D may harm bones, not help...at least that is what this article says.
To put those doses in context, 600 IU is the recommended daily amount of vitamin D for adults through age 70; 800 IU is recommended for people above age 70; 4,000 IU is considered to be the upper end of the tolerable intake level; and 10,000 IU is considered a megadose, well beyond what is typically advised, says Dr. Manson.
Some professional societies encourage people to take as much as 5,000 IU to 10,000 IU of vitamin D each day. This study provides new information that might prompt some to rethink those recommendations.
Stick to moderate amounts. "It's reasonable to take a small or moderate amount of vitamin D, such as 1,000 IU a day, if you're concerned about whether you're getting enough," says Dr. Manson. Supplements are best for people who tend to have little vitamin D in their diet.
Address unique risks with your doctor. Large doses of vitamin D (such as more than 4,000 IU a day) should be taken only under the advice of your health care provider.
Choose food over pills. If possible, it's better to get your vitamin D from food sources rather than supplements. To find a good source, check the nutrition labels on packaged foods to see how much vitamin D they contain.
Good food sources include fatty fish, such as salmon, tuna, and sardines, fortified dairy products, including milk, cheese, and yogurt, and cereals.
The way it reads is that people best keep close track of the calcium level in their blood if they are taking high doses of supplemental vitamin D.