Dietary supplements - too much of a good thing?

I've long believed that the fad of stuffing oneself with all sorts of vitamins, minerals and other odds and sods might be doing more harm than good. I'm glad to see that others are speaking out about it with greater frequency.  For example, the BBC reports:

This piece is about what we have learned about vitamin supplements in the last few years - if you are healthy, and you live in a country like the UK, taking multi-vitamins and high-dose antioxidants may shorten your life.

For most of us, for most of the time, they're unhealthy.

. . .

Looking at any one individual study won't be very revealing to answer the question of whether vitamin supplementation is good for you. They're densely scientific and the conflicts of interest can be very hard to spot.

For the answer you have to turn to what are called "systematic review papers". This is where independent scientists gather up all the available data and re-analyse it to answer big questions.

Here's what a couple of them say:

"We found no evidence to support antioxidant supplements for primary or secondary prevention [of diseases of any kind]. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing".

Just to be clear - "increase mortality" - that means they're killing you. These are powerfully bioactive compounds but they're not regulated in the same way as drugs. Whatever you think about the regulation there should surely be a warning on the pack if there's data saying they're bad for us.

The next question is - why are they bad for us?

. . .

Antioxidants provide a nice example. They soak up the very toxic, chemically-reactive by-products of metabolism called free radicals. These free radicals, left unchecked, can cause damage to DNA and may be linked to cancer.

Your cells are full of antioxidants but surely taking more would be better? Right? Keep those cancer causing radicals under control? Well, unfortunately, your body's immune system fights infections by using free radicals to kill bugs. Exactly what effect huge quantities of extra antioxidants could have on this is not clear but it's easy to imagine that it might not be good and you could get more infections.

Vitamin A is linked to increasing lung cancer in smokers. Excess zinc is linked to reduced immune function. Long-term excessive intake of manganese is linked to muscle and nerve disorders in older people. Niacin in excess has been linked to cell damage. And so on.

And it gets more complicated still when you start mixing everything up in one tablet. For example, different minerals compete for absorption. If you take large quantities of calcium you won't be able to absorb your iron. If you take large quantities of iron you won't be able to absorb zinc. If you take vitamin C you'll reduce your copper level.

So it's not just that taking lots of one thing is not good for you, it's that it may cause a dangerous reduction in something else even if you are also supplementing that.

There's more at the link, including a useful list of what's actually worth taking. Recommended reading.

Peter