The Surprising Downside:
There are many ways vitamin supplements will mess you up. Especially if you don't pay attention to the dosage. In 1999, researchers noticed that people who ate lots of beta-carotene (vitamin A) were less likely to develop lung cancer. They tested the theory by feeding 15,000 smokers the equivalent dose of six carrots a day, only to find that their doses were too large, and they were actually giving their test subjects cancer. In 2015, Norway's equivalent of the FDA verified that overdoing it with vitamin A may increase lung cancer risk for anyone with any kind of lung problems at all -- not only smokers.
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So if you're asthmatic and your mom makes you eat these things, you should probably call Child Services.
Other vitamin supplements don't fare much better. A study of 2256 women over 70 found that people who took mega-doses of vitamin D had 15 percent more fractures than those who took a placebo, because it turns out that our bodies consider high amounts of D toxic and start to break it all down, including the D already in our bones. Vitamin E doesn't fare much better: Several extensive trials have reached the conclusion that it seems to "increase mortality," and not because it gives you so much energy that you're out all day jumping motorcycles over bridges.
She won't want the D for a very, very long time.