Soy products may cause developmental and growth delay in infants and young children

This study was published in Pediatrics 2012 Sep;130(3):e699-702

 

Study title and authors:

Unawareness of the effects of soy intake on the management of congenital hypothyroidism.

Fruzza AG, Demeterco-Berggren C, Jones KL.

Division of Endocrinology, Department of Pediatrics, University of California San Diego, La Jolla, California, USA. afruzza@rchsd.org

 

This study can be accessed at: http://www.ncbi.nlm.nih.gov/pubmed/22908106

This paper describes two patients born with hypothyroidism (hypothyroidism is a state in which the thyroid gland does not make enough thyroid hormone) who were fed soy products and continued to manifest clinical hypothyroidism despite receiving recommended doses of levothyroxine (a synthetic form of the thyroid hormone thyroxine).

Patient1
(i) The first patient was diagnosed with hypothyroidism and treated with 50 µg of levothyroxine since six days of age while simultaneously starting soy formula.
(ii) At three weeks of age, she was clinically and biochemically hypothyroid.
(iii) Her soy formula was stopped and her levothyroxine dose decreased.
(iv) Three weeks later signs of hypothyroidism were resolving, and, by 10 weeks of age, her thyroid was clinically and biochemically normal.

Patient 2
(i) The second patient was diagnosed hypothyroid, received levothyroxine, and did well.
(ii) Over the next two years she began consuming soy milk and became profoundly hypothyroid even though her primary care physician had increased her levothyroxine dose to 112 µg/day.
(iii) She was switched to cows milk, and her thyroid function slowly normalized with decreasing doses of levothyroxine.

These two patients highlight the adverse affects soy products have on thyroid function and may cause developmental and growth delay in infants and young children. 

Soy may cause goiters in healthy people, especially the elderly

This study was published in Nihon Naibunpi Gakkai Zasshi 1991 May 20;67(5):622-9

Study title and authors:
The effects on the thyroid gland of soybeans administered experimentally in healthy subjects.

Ishizuki Y, Hirooka Y, Murata Y, Togashi K.
Ishizuki Thyroid Clinic.

This study can be accessed at: http://www.ncbi.nlm.nih.gov/pubmed/1868922

This study investigated the effects of soy consumption on thyroid function. The study included 37 healthy subjects who were given 30g of soybeans everyday and divided into 3 groups.

(i) Group 1 were given soybeans for one month.
(ii) Group 2 (average age 29 years old) were given soybeans for three months.
(iii) Group 3 (average age 61 years old) were given soybeans for three months.

The study found:
(a) In all groups thyroid stimulating hormone (TSH) levels rose significantly (high TSH levels may indicate an underactive thyroid gland).
(b) TSH levels in group 3 increased more significantly than that in group 2.
(c) Symptoms such as malaise, constipation, sleepiness and goiters appeared in half the subjects in groups 2 and 3 after taking soybeans for 3 months, but they disappeared 1 month after the cessation of soybean ingestion.

The author of the study, Dr. Yoshimochi Ishizuki of Aichi Medical University in Japan, concludes: "These findings suggested that excessive soybean ingestion for a certain duration might suppress thyroid function and cause goiters in healthy people, especially elderly subjects".