The immensely profitable vitamin industry depends on consumers believing that more is better. Although supplements are beneficial for people with nutrient deficiencies, there’s little utility in pills, injections and intravenous drips if you already get enough vitamins from your diet. The excess may simply be a waste of money, but it can become downright dangerous. When should the buyer beware?

It’s difficult to get too much of a single vitamin from food, according to Susan Barr, a registered dietitian who contributed to establishing the Dietary Reference Intakes, which are used across North America to establish nutrient needs, assess dietary status and create industry standards. (Those numbers on nutrition facts tables? They are based on Dietary Reference Intakes.)

“It’s always best to try to meet your needs for vitamins by eating a healthy diet,” Barr says. “However, there are some situations in which a vitamin supplement may be recommended, for example, vitamin D and vitamin B12 for adults over age 50, who may be deficient in these nutrients.”

And what about a daily multivitamin? Many people pop a pill as an “insurance policy” when their dietary habits are sub-par. Although sometimes unnecessary, a multivitamin is safe as long as the dose isn’t excessive; don’t take more than one a day.

“When choosing a supplement, a good general rule is to look for one that provides no more than 100 percent of the daily value for any nutrient,” Barr says. “That can help minimize the potential for harm.”

How much is too much?

Water-soluble vitamins, which include vitamin C and a range of B vitamins, are not stored in the body once ingested. Instead, they get excreted when you urinate. That’s why some vitamin naysayers tell supplement enthusiasts that they are “flushing money down the toilet.”

Even though water-soluble vitamins aren’t stored in the body, excessive amounts can still have damaging effects:

• High levels of vitamin B6 (more than 100 milligrams per day) can cause severe nerve damage, leading to loss of control over bodily movements.

• More than 2,000 milligrams of vitamin C daily can cause diarrhea and increase the risk of kidney stones.

• More than 1,000 micrograms per day of B-vitamin folate can increase the risk of vitamin B12 deficiency.

Fat-soluble vitamins A, D and E do get stored in the body once ingested. That means they are more likely to cause toxicity than water-soluble vitamins.

Excessive vitamin A can cause birth defects, liver problems and skeletal abnormalities, while excessive vitamin E can lead to hemorrhages and has been associated with increased risk of prostate cancer, Barr says.

And vitamin D? We need about 600 to 800 international units (IU) per day, depending on age, but this vitamin du jour is being taken in excess because it’s said to boost immunity and reduce cancer risk. Barr says it’s best not to exceed 4,000 IU per day. Higher intakes may have adverse health effects over time, including increased risk of cardiovascular disease and mortality.

False promises

Wouldn’t it be amazing if you could hook up to an intravenous (IV) vitamin infusion that would prevent aging, provide boundless energy and burn body fat? These are claims made by purveyors of IV vitamins, which are, quite literally, the flow of vitamins right into your veins.

“As far as I can tell, there is absolutely no evidence to support the IV therapy trend,” says Timothy Caulfield, professor and research director at the Health Law Institute of the University of Alberta and author of the 2015 book “Is Gwyneth Paltrow Wrong About Everything?”

This therapy is often marketed as a way of allowing vitamins to bypass your gut, Caulfield explains, and infuse the vitamins directly into the cellular space. “There is a lot of science-y-sounding hand waving, but very little actual science,” says Caulfield, who adds that he’s tried IV therapy and “felt no magical, energizing buzz.”

Depending on what’s in the IV drip and how often it’s administered, this practice has the potential to cause harm. It’s not regulated, and practitioners don’t need to be licensed. Oh, and the cost ranges from $100 to $300 per infusion.

Diet gurus peddle similar claims, promising that vitamin B12 shots will produce rapid weight loss. Of course, the injections are partnered with a low-calorie diet. Luckily, an excess of vitamin B12 won’t cause harm, except to your wallet.

“The public seems to love vitamins,” Caulfield says. “We can’t forget that it is a huge industry and there are many voices in popular culture pushing the more-is-better message. But, in fact, there is absolutely no evidence to support the more-is-better approach. Our body needs the correct amount, which, for most of us, can be obtained by eating a healthy diet.”