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Soy milk may be bad for your teeth

Robin Wulffson MD's picture
soy milk, acidity, teeth damage, Streptococcus mutans, oral health, dentistry

Many Americans drink soy milk with the belief that it is a healthier alternative to cow’s milk. However, a new study has reported that it may damage your teeth. Researchers from the University of Melbourne in Australia published their results online on May 17 in the Journal of Dentistry

The researchers note that soy beverages are water extracts of whole soybeans and are often promoted as a healthy alternative to bovine milk. However, the literature lacks studies evaluating the effects of soy beverages on oral health, especially their potential acidogenicity. (Acidognicity refers to the acidity of a substance.) Therefore, they conducted a study to determine the potential acidogenicity of a range of soy and bovine milk beverages. They chose four Australian-brand soy beverages, and two brands of cow’s milk for their experiments. The milks were each mixed with bacteria called Streptococcus mutans, which are found in the human mouth and commonly associated with cavities. In a laboratory setting (in vitro), acid production by S. mutans was measured in soy and milk beverages at a constant pH of 6.5 or 5.5; in addition, the decrease in pH over a 10 minute period was measured. (A lower pH indicates increased acidity; the pH scale ranges from 1 (high acidity) to 14 (high alkalinity).) The acid buffering capacity and calcium and phosphate concentrations (total and soluble) of the beverages were also determined.

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The researchers found that the rate of acid production by S. mutans in the milk beverages was five to six times lower at pH 6.5 than in the soy beverages and three to five times lower at pH 5.5. The pH fall in the presence of S. mutans over 10 minutes was negligible in the milk beverages; however, there was a significant decrease in pH in the soy beverages. This was also reflected in the lower buffering capacity of the soy beverages. The levels of soluble calcium in the soy beverages were lower than those in the milk beverages; however, the total calcium contents were similar.

The authors concluded that soy beverages have a higher potential acidogenicity than bovine milk beverages. The authors wrote: “Patients consider soy beverages to be a healthy, low cariogenic [tooth decay-causing] alternative to other beverages, including bovine milk. This study shows that soy beverages have a higher potential acidogenicity than bovine milk and therefore may have a greater potential cariogenicity.”

Take home message:

The cariogenicity (cavity risk) of most substances depends on how they are ingested. For example, drinking one glass of soy milk is unlikely to harm teeth; however, allowing a baby to sip from a bottle containing soy milk all day might be cause for concern. In contrast, cow’s milk is known not to promote cavities, regardless of how much is consumed. This is another study where the in vitro (laboratory) findings may prove to differ from the in vitro (human body) setting. The study was conducted in laboratory dishes; therefore, more research is indicated before researchers can determine whether soy milk actually damages teeth.

Reference: Journal of Dentistry

See also:
Six tips to keep your kid's teeth healthy
Ultrasonic toothbrush might revolutionize dental hygiene



Hi, It is important to note that the in-vitro expirements lasted 10 minutes, which is much, much longer than any food will stay in your mouth. Furthermore, the only things that this study concludes is that if you put soy milk in a petri dish with bacteria, it will grow, and it happens to grow better than dairy milk. Not article worthy, and should certainly not instigate lifestyle changes.