Doctors generally assume that North Americans are so well nourished that they never need to worry about supplements. In fact, they sometimes fuss that people who take vitamin pills could overdose on vitamin D or vitamin A, fat-soluble vitamins that are stored in the body. Is that worry justified?
How Much Vitamin D Do You Really Need?
Q. Both my husband and I have seen different doctors who recommend 4000 IU of vitamin D daily. (I’m on Prolia injections for osteoporosis.)
I don’t understand why the Mayo Clinic website recommends 600 IU but says some doctors recommend 1000 to 2000 IU. Is there a maximum amount?
The Official Recommendations for Vitamin D Intake:
A. The Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine sets recommendations for dietary intake. (You’ve seen this described as the recommended dietary allowance or RDA.) For adults under 70, the RDA is 600 IU. At 70, it jumps to 800 IU. The tolerable upper limit is 4,000 IU.
Your doctor can measure circulating vitamin D, called 25-hydroxyvitamin D. We think it makes sense to adjust your intake to keep your blood level of 25-hydroxyvitamin D between 30 and 50 ng/ml. You will find more information on this crucial nutrient in our eGuide to Vitamin D and Optimal Health.
Does Everyone Get Enough Vitamin D?
It turns out that many Americans have low levels of vitamin D circulating in their bodies. This is especially true of African-Americans, since dark skin takes more time to make vitamin D in the presence of sunshine. Those with adequate levels of 25-hydroxyvitamin D, the usual measured metabolite, have usually been taking supplements (Journal of Nutrition, April, 2015). What about people in other countries?
Chinese Elderly People More Likely to Lack Vitamin D:
One study compared detailed survey data from both the US and China (Scientific Reports, Dec. 23, 2019). The analysis showed that elderly Chinese people are more often deficient in this important vitamin than North American seniors. Because different factors lead to this outcome, the interventions would need to be distinct. As always, supplementation should be monitored to make it doesn’t result in an overdose on vitamin D.
Australians and Vitamin D:
Q. I’m glad you have been writing about vitamin D. Even here in Australia, many people have low levels of vitamin D.
White people are at risk for skin cancer, with 48 percent of skin cancers occurring in people of Celtic descent. (There are a lot in Australia). But we have gone overboard: we work indoors, apply sunscreen and wear hats. No wonder we end up low in vitamin D.
If you are an indigenous Aussie, either Aboriginal or Torres Strait Islander (TSI), and work for the government, you get free vitamin D tablets. A TSI friend is a lawyer and works indoors.
She is very dark-skinned and thus in need of more vitamin D. However, she spends her weekends doing the traditional TSI woman’s work of fishing while wearing very little clothing.
She told me that the government worried about ‘too much vitamin D’ when most of the new reef rangers were TSI people. Is that even possible?
A. If the reef rangers were taking vitamin D pills in addition to working out in the tropical sunshine, they could get too much vitamin D. But it would be from the pills, not from the sun exposure. The body has feedback mechanisms to keep it from making excessive vitamin D (Mayo Clinic Proceedings, April, 2012).
Can You Overdose on Vitamin D?
Excess vitamin D can indeed result in toxicity. This has happened, particularly when an infant or young child is given vitamin drops so they overdose on vitamin D (Journal of Steroid Biochemistry and Molecular Biology, April, 2015). Adults taking high-dose supplements can also overdose on vitamin D (Food and Chemical Toxicology, June, 2012).
You are right that many fair-skinned people in sunny climates can become low or even deficient in vitamin D by spending most of their time indoors. This happens in the southern US as well as in Australia.
This response was not specific enough for one reader who wanted more details.
Symptoms of Vitamin D Toxicity:
Q. You’ve written that “excess vitamin D can indeed result in toxicity,” but you did not mention what the symptoms of that toxicity would be. Those of us taking vitamin D supplements would like to know.
A. Many of the symptoms of vitamin D overdose are related to excessive calcium absorption and excretion–too much calcium in the blood and urine. The symptoms may include weakness, confusion, lack of appetite, nausea, vomiting and irregular heart rhythm. Some people suffer pain, dehydration, urinate too much and become very thirsty. People taking too much vitamin D, particularly if they are getting a lot of calcium, may develop painful kidney stones (NEJM, Feb. 16, 2006).
You can’t get too much vitamin D through food or sun exposure but taking high dose supplements could cause trouble. The tolerable upper limit of supplements for adults is 4,000 IU daily (100 mcg). Your doctor should be monitoring your level of 25-hydroxyvitamin D with periodic blood tests to make sure you keep it below 125 nmol/L (about 50 ng/mL).
You can learn more about the pros and cons of vitamin D and how much you need from our eGuide to Vitamin D and Optimal Health. It tells how to tell whether you need vitamin D supplements and what can result if you don’t get enough vitamin D.