Vitamins A, B, C, zinc: Which ones to buy and which to avoid

The messaging around vitamins became about preventing chronic diseases and helping you live your best life. Image / Getty Images

The vitamin and supplement industry makes billions of dollars each year telling us that we'll live longer, healthier lives by popping their pills.

But what is the best science on how helpful these products really are?

We need vitamins in our diet to be healthy. If you're severely deficient in vitamin C, you can get scurvy. If you have too little vitamin D as a child, you can get bowed legs - a condition called rickets. And not enough Vitamin A? That could make you go blind.

In the 1920s and '30s, when scientists started discovering these seemingly magical vitamins, people were so excited about them that they added them to food, like flour and dairy products. Fortifying milk with vitamin D helped lead to an almost complete eradication of rickets in the US. Soon, companies started turning vitamins into little pills and bottling them. And they were an immediate hit.

But, the messaging around vitamins quickly shifted. Vitamins were no longer just protecting you from scurvy or rickets, but preventing chronic diseases like dementia and heart disease, and helping you live your best life. The big question is: do vitamins have that power?

To find out, scientists track large groups of people to see if taking vitamins reduces the risk of getting certain diseases.

What happens when you extract vitamins from fruit and vegetables and pack them into one big multivitamin? Getty Images

When vitamin B supplements are put under the microscope researchers find "no evidence" that they prevent heart disease, strokes or cancer. Vitamin B also "does not appear to improve cognitive function" in healthy people, or those who are starting to go a little dotty. As for helping people with depression? It wasn't particularly useful for that either.

But when it came to improving depression, or dementia the researchers say more work is needed.

There is evidence that taking vitamin C and zinc lozenges could help you get over your cold a bit faster. "The evidence for zinc lozenges is very strong," says Harri Hemilä at the University of Helsinki in Finland. But, there's not good evidence these supplements will keep you from getting sick in the first place.

THE VITAMIN D PANDEMIC

And maybe you've heard we're experiencing a pandemic of vitamin D deficiency. Even the US Rapper, Ludacris is worried about it. (Well, he might have been rapping about something else.) But, the story with vitamin D is complicated.

To know if we are low on vitamin D, scientists would have to agree on one thing - exactly how much vitamin D we need. And perhaps surprisingly, scientists are still debating this. "There is a lot of animated discussion right now," said Professor Katherine Tucker, a nutritional epidemiologist at the University of Massachusetts in Lowell.

Part of the debate is that it's unclear what vitamin D is beneficial for. A team brought together by the Institute of Medicine in the US several years ago wrote that vitamin D was important for bone health. But, they said, other conditions, like diabetes, depression or cancer, could not be "linked reliably or consistently" to vitamin D. Yet, other scientists disagree.

What about vitamin E? "The new evidence says, no, don't take it," Professor Tucker said. A decade ago there was a big push for people to take vitamin E, but then scientists realised it actually wasn't that helpful and might even increase your risk of some kinds of cancers.

Finally, we know that eating a diet full of fruits and vegies packed with different nutrients can help us live longer and prevent heart disease. But what happens when you extract those vitamins into one big multivitamin? "There's been some big studies that show they didn't really have major effect," Professor Tucker said.

One large study recruited 14,000 older men, and gave half multivitamins while the other half were given a placebo. The men were tracked for more than a decade. And, after all that work? There was no difference in rates of heart attacks and heart disease between the two groups.

Curiously, the men who took the multivitamins had a slightly reduced risk of cancer. But the researchers said we shouldn't get too excited, because other large studies have been really mixed.

But Professor Tucker wasn't ready to throw out the multivitamins just yet as she said a few large studies into multivitamins have been done in doctors and they might have better diets than your average Joe. So, for people who aren't eating so well, "it doesn't hurt to take a multivitamin for insurance," she said,

Overall, it doesn't look like vitamins in a pill do all that much. But studying the benefit of taking vitamins in large groups of people is really tricky, and all the research we have can't really tell us whether you, personally, should be taking vitamins or not.