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Shereen Jegtvig, MS

Does Sugar Really Hurt Your Immune System?

By October 5, 2009

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Or could it really due to obesity? The idea that eating sugar is bad for your immune system has been a common belief since a study published in 1973 stated that blood from volunteers fed sugar was less able to fight bacteria than blood from subjects not fed sugar.

I have to admit I've always labored under that assumption and so have other experts, like Dr. Jim Sears, one of the co-hosts of the popular daytime show The Doctors and Dr. Lisa Hark mentioned it my my article on eating foods to help prevent colds and flu.

Today I came across an article in USA Today questioning that belief. Some experts tell us that the evidence from 1973 isn't all that compelling (actually it was all done in the lab - not in the body) and that no research since that time has been able to back up the claim. A quick search or two in PubMed doesn't bring up anything, so maybe the idea that eating too much sugar can increase your risk of getting colds and flu is overblown.

Since I was searching through PubMed, I decided to look at obesity as a risk for influenza and found an interesting article from Europe that examines various risk factors for dying of H1N1 influenza. The authors found that obesity appears to increase the risk of dying from an H1N1 infection (though it doesn't say anything about obesity and the risk of catching H1N1).

The authors don't know why being obese could increase the chance of dying from H1N1. It could be due to obesity complicating the treatments used in severe cases, or it could be due to diabetes that occurs commonly alongside obesity, but there is also the possibility that obesity affects the immune system directly. According to a study in 2007, obesity messes with the immune function of mice. Research will have to be done with people to understand more about obesity's role in H1N1 mortality.

So I guess in a round about way, I might still believe sugar is bad for your immune system, but only if you eat so much of it you become obese. A little bit of sugar is fine, as long as you stay within your daily calorie need and get all the healthy foods you need too.

October 7, 2009 at 11:32 am
(1) Sara says:


Sugar feeds “bad” intestinal bacteria. Proliferation of this bad bacteria causes lowered immunity. Our immune system resides largely in our gut, where the bacteria resides. Of course the subjects in the study couldn’t fend off pathogens — their body was already in a fight against the bacteria caused by sugar. It’s really that simple. This is life-changing information people need to hear. Please look into this.

October 7, 2009 at 12:09 pm
(2) Janis says:

Sugar is BAD!!! Read Dr. Nancy Appleton’s book on how she battled a sugar addiction and how it caused all kinds of ill health for her. She tells, scientifically, how sugar causes the body to lose it’s balance by throwing off the mineral balance. I have also read that sugar depletes our body’s vitamin C stores, which fights off infection. So for me, the less sugar I eat the better off I am!!

October 7, 2009 at 3:07 pm
(3) Blissful says:

I eat sugar every single day….I bake all the time and I make my own candy and eat only Callebaut chocolate. I am not obese and otherwise have a good natural whole food diet.
I can’t digest the artificial sweeteners and they run right through me. I also have chemical sensitivities as the result of almost dying of a natural gas leak 22 years ago….so I never eat ANY food with chemicals.
I drink a quart of kefir in 2 days and it is a routine part of my daily diet. I buy it by the case and drink a full 12 quart case every month. Since I started that about 4 months ago my IBS has calmed down a lot and my digestion in general is way better.

Personally, I think it’s the chemicals that are added to sweet foods ( and all processed foods) and not the sugar itself that makes people sick.

I haven’t had a cold for 6 years, or the flu for 12 years. So all the hype about sugar being so bad really mystifies me. I’m almost 60 years old and have had a sweet tooth all my life. My teeth are good too!!

Can’t anyone see the connection between feeling rotten and eating chemical food additives????

October 7, 2009 at 3:57 pm
(4) Ted says:

I battled with Colitis for 25 years until my large intestine became pre-cancerous and it had to be removed. Prior to my surgery I tried everything under the sun to help my symptoms. Doctors only prescribed drugs that had little effect or made me feel worse. I didn’t want a “band-aid” as it were, I wanted the problem fixed. Yet no one could really tell me how to do that. The problem even spread to my liver.

I am not a doctor, nor do I have any medical training, however I have discovered that sugar definitely plays a role in IBS! Once the balance between good bacteria and bad bacteria gets out of wack, sugar and an acidic diet go hand in hand to take the situation out of control.

Today, I have reduced my sugar intake drastically and limit salt. I eat a more balanced pH diet and I have recently started drinking a shot of apple cider vinegar before bed.

I’m still not a 100% but a massive improvement overall and currently on no medication.

If you have IBS – rid your diet of as much sugar as you can and try to get your intestinal bacteria back in balance. With some research i asked my doctor to prescribe me an antibiotic called Flagyl and immediately followed it with a short course of probiotic. Worked for me.

October 7, 2009 at 4:41 pm
(5) Shereen says:

Sara – it is true that bacterial overgrowth is often associated with an inability to digest some type of sugar. A common example is lactose intolerance, which occurs when a person can’t digest milk sugar. Other inflammatory disorders of the digestive tract can cause problems with absorption as well. Fortunately, foods with friendly bacteria, such as yogurt, can help keep the bad bacteria in check.

October 7, 2009 at 4:49 pm
(6) Shereen says:

Blissful – thanks for your comments. Sweet foods certainly may have lots of additives that people are not comfortable consuming and processed sugary foods are frequently not very nutritious, but high in calories, and may also contin too much trans and saturated fats and way too much sodium.

It sounds like you found the perfect balance of enjoying sweets you make with high quality ingredients and eating a healthy diet.

October 7, 2009 at 4:51 pm
(7) Shereen says:

Ted – I’m glad your dietary changes helped. Probiotics can do so much to help digestive probems.

October 8, 2009 at 11:50 am
(8) david White says:

Talk to any public school teacher, like me for over 30 years, and you will have all the proof you’ll ever need. Ask them about the the behavior and health of students after halloween and now easter holidays. I’m a number nut and my records show 50 to 60 % increase in students out with sickness and the out of control behavior in my classes went from one incident/week to over 20.

October 13, 2009 at 11:41 am
(9) Carrie says:

As glucose competes with Vitamin C for entry into the cells and also affects Vitamin C already present and Vitamin C is a factor relating to immune function, I’m wondering if you would comment on the effects of sugar on the Vitamin C component of immune function.

Ottoboni F. Ottoboni A. Ascorbic acid and the immune system. The Journal of Orthomolecular Medicine 2005;20(3):179-183

October 13, 2009 at 1:12 pm
(10) Shereen says:

David, do you also notice any behavioral changes? I know a lot of teachers and parents (including me) have observed behavioral changes after kids eat a lot of sugar, but that hasn’t been reproduced in any good research studies.

Anecdotally, my daughter would go just nuts after eating something sugary when she was little. Maybe it was the sugar or maybe she was just excited to get something sweet and yummy to eat. It drove me nuts though, when she would get an ‘unauthorized’ sugary treat.

October 13, 2009 at 1:23 pm
(11) Shereen says:

Carrie, both glucose and vitamin C compete for insulin, and some weird things can happen. A person who takes large amounts of vitamin C (like 4000 mg or so) can actually appear to be diabetic because it may keep the blood glucose levels elevated.

You posit that large amounts of sugar would break down and the glucose half would block vitamin C from being absorbed, thus affecting the immune system. I’m thinking that in a person who is diabetic or pre-diabetic (who has insulin problems) might have an issue here, but again this diabetic or pre-diabetic condition is probably due to obesity (unless, of course, it is type I).

I am thinking that an otherwise healthy person makes enough insulin to take care of both the glucose in a candy bar and their vitamin C needs. Or maybe vitamin C shouldn’t be taken around the same time as the candy bar, but maybe that candy bar eaten in the afternoon won’t have any affect on the vitamin C eaten in the red peppers later on at dinner.

Plus sugar is only half glucose (or less in the case of High Fructose Corn Syrup), so following Ottoboni’s idea, bread, pasta and other starchy foods would be much worse for your vitamin C levels than sweets.

What I am currently searching for is a study that might measure the vitamin C levels in subjects and then make comparisons by their diets, weight, presence of disease, etc. But I haven’t found anything yet.

Thanks for your comment!

November 3, 2009 at 3:30 pm
(12) Jeanne says:

Dr. John Ely also had the Glucose Antagonism Theory. Sugar and vitamin C (the big immune system boosting vitamin) enter cells through the same insulin mediated pathway. If you eat too much sugar, the paths get crowded, like too many people trying to enter a building by the same doors; sugar wins, and it enters and vitamin C is left out. It’s still in the theory stages and I have not been able to find research proving it, but it’s a really intriguing theory about why eating excessive sugar suppresses immune response. It could also have bearing on why some of the obese people aren’t doing as well with H1n1 or seem to have compromised immune systems – if their circulating glucose is high (ie, perhaps pre-diabetic range, as happens with many overweight people) it might be crowding out all that good vitamin C. Still just THEORY but really interesting.

November 4, 2009 at 1:22 am
(13) Mike says:

You people have missed the entire point of the article. Everything you have heard parroted by TV doctors has been based on a single, inconclusive study. Just because you’ve heard something multiple times does not mean it is correct.

Ted you may want try cutting out gluten from your diet. Alot of IBS cases have turned out to be Celiac disease where the presence of wheat gluten triggers and auto immune response response, resulting in IBS symptoms. There are lots of good gluten free products on the market.

February 16, 2010 at 7:01 pm
(14) stuart says:

Just found a product called ‘organic coconut sweetener’ its makers say its made from coconut flower sap, low in calories, low on the glycemic index (3.5), contains vitamins and minerals, can be used by diabetics.
Its tastes good but is expensive.

May 24, 2010 at 2:46 am
(15) Helen says:

I stopped eating sugar five years ago, and never had a cold or a flu since. I was never overweight, didn’t eat junk food , didn’t have diabetes, but before I stopped eating sugar, I was guaranteed at least a couple of colds and one bout of flu every year.

October 31, 2011 at 2:43 pm
(16) Elisabeth A. says:

Every day for the past 2 yrs. I have been eating a bad diet of yogurt for breakfast and cookies and then nothing til at nite when I would eat some take out and then would eat at least 15 of those large chocolate covered biscottis and some chocolate cake. I ended up gaining 30 pounds and on my 5 foot frame 160 lbs. is a lot. I then started having no energy, aches and pains all over, my hair fell out so much that I would cry. Then I’d get sick a lot, my knees would click and ache. I realized my immune system was weakened by all the sugar I had been eating every day for yrs. I was addicted to these cookies and would spend about $25 a day on them and cake. I’m 44 years old and did serious damage to my body from eating all that sugar. I am now 2 weeks sugar free and its a struggle to stay off it but I know that my life and health depends on it. I am feeling a bit better. My mind isn’t foggy anymore. I have more energy, am sleeping better and have already lost 5 pounds. Hair is still falling out and I’m still achy and knees hurt but I was told I need to give my body more time to detox and heal. Its only been 2 weeks. Also I am missing the sugar less and less each day. The first week was so hard that I felt as if I was detoxing off heroin. All I would do is dream of the cookies and cravings were unbearable but I was so sickly that I knew I had to do this sugar detox or die. It was that bad. So in my case yes sugar was a poison and totally screwed up my health. Never again. Only healthy food for me from now on and vitamins, omega 3,6,9 and flax. This whole thing started cause of my depression over having my house burglarized 3 yrs ago and them taking everything including all my jewelry and life savings from the floor safe. I was at work at the time. I was devastated.

March 1, 2012 at 9:44 pm
(17) Darian says:

David White, What school do you teach at, and in what state. I am doing a project, and my teacher would like me to site your school. Is that ok?

June 1, 2013 at 9:14 pm
(18) Warren Dew says:

Are we talking about the same 1973 experiment? Sanchez, AJCN? It’s about the only actual experiment in this area that isn’t entirely in the laboratory, as actual humans ingested the sugar before the neutrophils (white blood cells) were extracted.

That experiment did also test diabetics, and found reduced neutrophil activity even from fasting diabetics. That’s consistent with your observation that diabetics seem more susceptible to H1N1 – diabetics are more vulnerable all of the time, while normal people are more vulnerable only for a few hours after eating sugar.

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