Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started
My Medicine

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Health & Baby

Font Size

Study Suggests Effects of Products in Soy-Based Formula on Thymus Size

WebMD Health News
Reviewed by Gary D. Vogin, MD

June 29, 2001 -- A small study in animals suggests that a substance found in soy and soy-based infant formula could have an adverse effect on growth of the thymus, which is critical to immune function.

But the study researchers -- as well as other nutritional experts -- are quick to say that the findings do not prove that soy-based formula is bad for babies.

"It's way too early to say if there is a smoking gun," says author Srikanth Yellayi, DVM, a doctoral student at the University of Illinois at Champaign. "Until we do much more research, it's too preliminary to say there is any danger."

But Yellayi's research suggests that a substance known as genistein -- an estrogen-like hormone that is found naturally in plants but not in humans -- affects the size and development of the thymus at doses that are comparable to what would be found in soy-based infant formula.

Yellayi tells WebMD it has previously been established that sex steroids, such as estrogen, have an effect on the thymus. "What we have shown is that the estrogen in soy is also having an effect on the thymus and could impair the immune system," he says.

In the study, five mice were injected with genistein, five were injected with estrogen, and five mice were given no treatment. After 21 days, the mice were compared by looking at the size of the thymus.

As expected, the animals that were treated with estrogen experienced a 50% reduction in the size of the thymus compared to mice who received no treatment. More unexpected were the results for the mice treated with genistein: They experienced a 20%-80% decrease in thymus size, depending on the dose.

The study was presented at a recent meeting of the Endocrine Society in Denver. Paul Cook, PhD, a professor of physiology at the University of Illinois, was a co-author of the study.

Yellayi says the effect was seen with doses as small as .02 mg a day -- comparable to the level of exposure for babies being fed with soy-based formula. "Thus, soy formula, which accounts for 25 percent of formula sales in the U.S., may be capable of inducing deleterious effects on the developing human infant thymus and immune system," say Yellayi and Cook.

Baby's First Year Newsletter

Because every week matters, get expert advice and facts on what to expect in your baby's first year.

Today on WebMD

mother on phone holding baby
When you should call 911.
parents and baby
Unexpected ways your life will change.
baby acne
What’s normal – and what’s not.
baby asleep on moms shoulder
Help your baby get the sleep he needs.

mother holding baby at night
mother with sick child
Chinese mother breast feeding newborn baby girl
Track Your Babys Vaccines
Baby Napping 10 Dos And Donts
Woman holding feet up to camera
Father kissing newborn baby
baby gear slideshow