An interview with Dr. Shanna Swan
Shanna Swan, PhD, is an epidemiologist at the Icahn School of Medicine at Mount Sinai in New York City. Her new book, Count Down, chronicles how chemicals in our air, food, water, homes, and personal care products are threatening sperm counts and jeopardizing human reproduction. Shanna will discuss her book and her work at a webinar sponsored by the EaRTH Center and PRHE on Wednesday, April 28, at noon PT (3:00 PM ET), register here.
Q. Why did you want to become an epidemiologist?
My doctorate is in statistics, a long way from epidemiology. I got my doctorate from University of California, Berkeley, and was offered a position as professor, but I could not take it because I was about to marry someone who was on the faculty, and married couples were not allowed to work in the same department. My advisor suggested I wait until I retire to get married, but I got married and had to leave. So that’s how I left statistics and went to the Kaiser Division of Research, working on whether oral contraceptives changed a woman’s body. I started to publish works on the relationship between cervical cancer and oral contraceptives and how cervical cancer is related to sexual activity. Then I joined the California Department of Health which was looking for someone who could be an epidemiologist and a statistician.
My first assignment was to go to Southern California and look at this community where an activist had claimed that something in the water was leading to too many birth defects and miscarriages. It was in Los Paseos, which was near a semi-conductor plant, where 80,000 gallons of toxic waste had leaked from an underground storage tank and contaminated the drinking water of local residents. So that was how I came to epidemiology.
Q. Did you find a connection?
Yes, but it’s complicated. We did a study and found there was a significant excess of spontaneous abortions in that area compared to an unexposed area. We did a second study with two different communities — one exposed and one not exposed – and were surprised to find that the miscarriage rate in the new exposed community was extraordinarily low. Very confusing, so we figured something might be going on unrelated to the spill. We discovered solvents in the drinking water were a problem and it turned out the issue was not this particular tank. Numerous studies later got me into studying sperm.
Q. Your new book, Count Down, tracks how our “modern world is threatening sperm counts” and “imperiling the future of the human race.” What brought you to that conclusion?
What triggered the book is a publication of a paper in 2017 which reported the results of a meta-analysis of all studies with estimates of sperm counts that were published in peer-review English language journals and conducted between 1973 and 2011. Our goal was to see whether sperm count had changed over time worldwide. My colleagues and I did this because 20 years earlier a Danish study had been published showing sperm count had declined dramatically in the prior 50 years, so ours was not the first study to report this finding. In fact, in 1992, the National Academy of Sciences asked me to look at the 1992 Danish paper. I didn’t believe its conclusion, so I examined all the underlying studies and took six months to analyze them. How were the men recruited? What were their ages? What was their sperm count? I was trying to find what would explain away the decline. But none of these factors mattered; the slope remained the same. Bottom line, I had to believe it because I had proved it to myself.
So, once I believed it, I started asking why. Why is sperm count declining? I got NIH funding to do a large study to look at semen quality in four cities in the U.S., using the same methods at all sites and showed that environment did matter. The biggest contrast was between central Missouri, which is rural and agricultural, and had half as many moving sperm as men in Minneapolis. That study by our group, and similar studies by other groups, showed that environment matters for sperm quality. At that point, I was convinced that sperm counts were going down and environment played a role.
A colleague, Hagai Levine suggested that we update the 1992 Danish study. We ended up with seven co-authors all working extremely hard for two years because the findings turned out to be huge. What we published in 2017 was the result of that meta-analysis. It confirmed the Danish study and showed that sperm count had continued to decline in North America, Europe, Australia, and New Zealand. Over those 39 years, total sperm count in Western countries had declined 59% and sperm concentration by 52%. Huge news. Unlike the original Danish study that was questioned and ignored, this one was not. Front pages, all over the press. Then an agent asked if I would write a book.
Q. What are the chemicals our readers should be most concerned about and how can we get them out of circulation?
Factors such as smoking and binge drinking are important for reproductive health and semen quality. If you look beyond that, then it’s largely chemicals, and it’s those that have the ability to affect hormones, which drive reproductive health. So, I’ve focused on chemicals that affect hormones like testosterone and estrogen.
When I got into this, in 2000, I had not heard of phthalates. A friend from the CDC, John Brock, said, “You should study phthalates.” Indeed, 95% of the population is exposed to multiple phthalates — everyone has these in their bodies. Then he told me that the National Toxicology Program had studied these and found that certain phthalates were related to problems in genital development of male offspring in animals. These chemicals had such a significant impact on male sexual organs, that it was given a name: the phthalate syndrome. So, how would I study that in humans? It’s challenging since no one is born without these chemicals in them.
That led me to conduct the Study for Future Families. I had saved women’s urine for this study (not sure at the time why I saved their urine), and I used it to measure how much phthalates women were exposed to when pregnant. Then with an NIEHS grant, I brought back the children of these women and examined their genital development, using methods consistent with what was done in the animal studies. I published those results in 2005, and it was a big story because this was the first time that maternal exposure to phthalates was shown to disrupt human fetal development, and the first time anyone had looked for the phthalate syndrome in humans.
To look at this we measured ano-genital distance (AGD) (the distance from the anus to the genitals, an important marker that had been used in the animal studies), and found it was diminished in males exposed to higher phthalate levels. We also found the penis was smaller and the boys were more likely to have undescended testicles. In this, and a second study, we demonstrated the phthalate syndrome in humans.
Q. What can businesses and policymakers do about this problem?
It starts with the chemical manufacturers. They have to begin removing from commerce the chemicals that are harming us and replace them with safer chemicals that are: 1. not hormonally active at low doses, 2. not persistent in the environment, and 3. tested for safety, which most chemicals in commerce are not. The overarching demand should be that safety is established prior to marketing.
Q. You’ve talked about how we’re seeing major changes within just two generations. If endocrine disruptors are cumulative, how do we get out of this mess?
In our book we talk about solutions, and I start with food, food packaging, and food preparation. Best to buy unprocessed food, if possible, to avoid chemicals introduced in processing. Food that goes through soft tubing will absorb phthalates. Shop at local farmers’ markets if you can. Organics are better, not just to avoid pesticides, which are related to men’s low sperm count, but also to avoid phthalates used as additives to increase absorption of pesticides. There are real equity issues involved here. I also avoid eating food from tin cans. Even if it’s labeled “BPA free,” it could contain “bad actor look-alikes” (BPF and BPS). Then store your food in glass, metal, or ceramic, not plastic. If you have to use plastic, look at the bottom of the container and check the recycling code in the triangle; 3, 6, and 7 should be avoided. Plastics with codes 1, 2, 4 and 5 are safer, but really, there’s no guarantee that any of these are safe. If it has no recycling code, be suspicious. And avoid microwaving in plastic of any kind.
Sometimes we get exposed in ways we don’t even realize. In the neonatal intensive care nursery (NICU), babies get nutrients through plastic tubes that contain phthalates. We did a study where we saw that the number of tubes coming into a baby in the NICU is proportional to the amount of phthalate in a baby’s urine. It’s really scary and depressing. Even organic dairy products may be collected through soft flexible tubing.
Avoid fragrance. These have phthalates and parabens. Personal care products more generally contain tons of chemicals allowed in this country that are not allowed in the European Union – they’ve banned 11,000 and we’ve banned 11. Look in Count Down at the list of resources we have. Check your products at Environmental Working Group (EWG), where you can look up products by name. We need to open our eyes to where we are getting exposed. But don’t let perfect be the enemy of good. You can’t do everything, but do what you can.