Tuesday, 19 May 2009

Vitamin supplements undo benefits of exercise

First, some facts:

Exercise has loads of health benefits including decreasing your risk of insulin resistance and type 2 diabetes by making your body’s cells more sensitive to insulin.

The more sensitive your cells are to insulin, the easier it is for the glucose (sugar) that’s in the foods you eat to get used up by your body. When your cells become insensitive or resistant to insulin, the glucose doesn’t get used up by your body but instead stays floating in your blood, causing high blood sugar. You body cries out for the glucose it needs to function causing your pancreas to over-compensate and produce even more insulin. This combination of insulin-resistance and insulin over-production by the pancreas leads to diabetes and/or obesity, increased risk of heart disease.

Inhaling oxygen produces free radicals. These free radicals attack the body causing you to age and also causes illnesses like heart disease and cancer and, eventually, death. 2-3% of the oxygen consumed by our cells is converted into free radicals.

When we exercise, we use lots of oxygen, increasing free radical production and all the stuff that goes with that.

Antioxidants are those highly publicized substances found in plant foods like fruits and vegetables that neutralize free radicals.That's why eating a diet rich in fruits and vegetables is good for you!

The Study:

It seems logical that taking supplemental antioxidants, like Vitamins C and E, would reduce the harmful effects of the free radicals produced during exercise and promote longer life and better health, right?

That’s what German researchers thought when they decided to observe 40 young healthy men (half were pretty sedentary and half exercised about 6 hours a week)- randomly assigned, half took a combination of 1000mg of vitamin C (btw, the recommended intake is 75mg and 90mg/day for women and men respectively) and 400 IU of vitamin E (recommended intake is 33 IU/d)- these amounts are commonly found in over-the-counter supplements- for 4 weeks while the other half didn’t. Both groups exercised, supervised, 85 minutes a day, five days a week for the 4 weeks of the study (workouts included biking, running and circuit training).

What they Found:

The exercisers NOT taking the antioxidants did have more free radicals floating around in their bodies but had a significant increase in insulin sensitivity (a good thing), as predicted. However, there was no increase in insulin sensitivity in those taking the antioxidants... but there were less free radicals.

It seems that the supplemental antioxidants prevent the health benefits of exercise when it comes to diabetes prevention. According to the authors, the free radicals produced during exercise are actually a good thing as they activate the body’s defense systems against exercise-induced stress, allowing it to use carbohydrates (glucose) more efficiently, thus helping to prevent diabetes and possibly other diseases. Taking supplemental antioxidants blocks this process and therefore health promoting effects of exercise.

Bottom Line:

Antioxidants like Vitamins C and E found in food protect our body from damage and help prevent diseases like cancer- this doesn’t change. However, taking high doses in supplemental form can be harmful.

As I’ve said before, if you're healthy and eat a balanced diet that includes a variety of fruits and vegetables, you don’t need supplements!

Previous blog entries that drive this point home: Vitamin Supplements Can Kill You & Get Rid of your Multivitamin and Eat Real Food!


Gina said...

YES!!! I love this post!! I took a molecular biology course that focused on antioxidants last quarter and we discussed exercise induced free radicals, and vitamins C and E. This was a great study review, and it definitely clarified some things. I was always confused as to WHY the free radicals that form during exercise are actually not bad....thanks for the info!

Sybil Hebert, RD said...

Thanks Gina!