I’ll admit to being a parent who chooses “selective vaccination” for my children. But I’m also a scientist, holding a degree in biochemistry, and having worked in research for 6 years after graduation. As such, I have to also admit that I OFTEN cringe at claims I hear from people who are opposed to vaccinations.

One of those claims is a concern that the Polysorbate 80 (also called “Tween 80”) that is in many vaccines and in the Vitamin K injection given to newborns could cause infertility down the road.  This concern comes out of a study that was done with newborn rats that found that injections of Polysorbate 80 caused fully grown rats to have smaller uteri in comparison with their ovaries.

So why in the heck is Polysorbate 80 even in vaccines and the Vitamin K shot? Polysorbate 80 is an emulsifier–meaning it helps oil to stay dispersed in water. This is important when administering “fat soluble” vitamins like Vitamin K.

Okay, so there is a good reason to have it in the shots, but do the benefits outweigh the risk? Infertility is a pretty big deal! To understand this, we need to understand if there is really enough Polysorbate 80 in these shots to cause negative effects. It is often said that “poison is in the dose.” This is true. Even pure water will kill you if you drink enough of it. Pure oxygen will kill you as well.

There is 10 mg of Polysorbate 80 in a Vitamin K shot that is shown in one video claiming to show how dangerous the Vitamin K shot is. This would be given to a newborn who is about 3.5 kg (7 lbs 11 oz), so would be a dose of about 3 mg/kg of body weight.

The study done on rats that found Polysorbate 80 had effects on fertility involved giving 100 mg of Polysorbate 80 to rats that were 4-7 days old. I can’t find an exact weight on rats of this age, but I can find that newborn rats weigh 6-8 g. If we even assume that the rats double their birthweight to 12-16 g by 4-7 days old, we are then looking at dosing that is at best 6 mg per GRAM of body weight.

That would be 6000 mg per kg (6g/kg). So dosing that is approximately 2000 times higher than what is given in the Vitamin K injection. I think it is a pretty far stretch to think that these two doses have the same effects. In the particular video I was recently watching, the speaker made a distinction between injected vs injested administration…which is a fair point. But I’ll also point out that in the rat study on fertility I linked to above, the Polysorbate 80 was injected into the rats. As far as oral dosing goes, Polysorbate 80 has been used in food products for over 50 years, and was extensively studied in the 1950’s, mixing it into rat diets in larger quantities than would be expected to be found in human diets. At daily diets that were 5% Polysorbate 80 (which would be about 28,400 mg in a newborn–compared to the 10 mg one time dose in the Vitamin K shot) , there was no affect on fertility, it took levels that were up to 20% of the daily diet (about 113,000 mg in a newborn) to have an impact on fertility.

In fact, in looking at several different versions of the Material Safety Data Sheets for Polysorbate 80–which are generally written with an expectation of people working with 50 gallon drums of the stuff, I find it being referred to as “low hazard” over and over.

The Vitamin K shot on the other hand, has been shown to prevent death in infants from hemorrhagic disease of the newborn.