Does excess sugar affect your immune system/inhibit vitamin C absorption?

Question

There are lots of websites out there with domain names containing words like "healing" and "natural remedy" that suggest that your immune system can be affected by excess sugar. Others also suggest Vitamin C is affected by too much sugar.

Sugar depresses the immune system.

We have known this for decades.

[...]

The health dangers which ingesting sugar on an habitual basis creates are certain. Simple sugars have been observed to aggravate asthma, move mood swings, provoke personality changes, muster mental illness, nourish nervous disorders, deliver diabetes, hurry heart disease, grow gallstones, hasten hypertension, and add arthritis.

—Sugar's effect on your health

Is there any scientific truth to these claims?

Answer 1

Large amounts of excess sugar in the gut can prohibit the absorption of Vitamin C ( http://www.annualreviews.org/doi/abs/10.1146/annurev.nutr.25.050304.092647), and Vitamin C is an antioxidant, so the argument can be made that excess sugar affects your immune system.

However, it is not clear how much sugar is classed as 'excess'. These things are often blown out of proportion: people who go on about how terrible caffeine is for you often cite research where rats were given massive doses of it, like that proves one cup a day will see you to an early grave.

Also, antioxidants are far from being a panacaea. They are supposedly beneficial in that they destroy free radicals in the blood stream. However, free radicals are themselves essential in the immune system's destruction of pathogenic bacteria.

As ever, the best advice is use your common sense. Eating a lot of sugar is bad for your teeth, and if you don't burn off the calories gained from eating it you'll probably become overweight, with all the health risks that entails.

But sugar in moderation is not necessarily a bad thing: recent studies have even shown that the pleasure derived from eating comfort foods, and the subsequent benefit to your mental health, outweighs the negative aspects of eating them. ( http://www.upi.com/Health_News/2011/03/27/Meatloaf-mashed-potatoes-fight-loneliness/UPI-79641301252021/)

Answer 2

There is a scientific basis for it, in the form of a 1973 paper in the American Journal of Clinical Nutrition, which showed that for several hours after a person ingests sugar, neutrophils, a form of white blood cells, were less effective at engulfing bacteria.

http://ajcn.nutrition.org/content/26/11/1180.full.pdf

Of course, that leaves open the question of just how important that loss in neutrophil activity is to disease resistance.