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'Declines in Sex Ratio at Birth and Fetal Deaths in Japan and U.S., but not in African Americans'
Frequently Asked Questions
Studying patterns of various health outcomes in populations can reveal significant changes in the environment and in the level of environmental toxins to which an individual is exposed. More information.
So It Begins – Before and During Pregnancy
While each of us is born alone, our health can reflect the things that happen to our mothers and father before we were conceived, as well as during early pregnancy. Our new work shows that the sex of children at birth can be influenced by a number of avoidable environmental factors. How?
The Sex Ratio’s Downward Spiral?
Whether declines in births of baby boys are connected with a number of puzzling patterns in male reproductive health is a matter of serious concern. Several studies—some from the 1980s, early 1990s, and our new paper –show that over the past two to three decades the births of baby boys have declined in Japan, the U.S., England and Wales, Denmark, Sweden, Finland, the Netherlands, Germany, Chile, Argentina, Brazil, Bolivia, Peru, Paraguay, Ecuador, Venezuela, Colombia, and Costa Rica. Since 1970, the proportion of white boys born in the U.S. and Japan has dropped from 105.5 boys per 100 girls to 104.6 and from 106.3 to 104.97, respectively. Even such tiny drops in the sex ratio can amount to thousands of missing baby boys. For example, if the sex ratio in the U.S. and Japan had remained at its 1970 rate, almost 137,000 and 125,000, respectively, of the baby girls born between 1970 and 2000 would have been boys. No one knows why this is happening, but some interesting clues exist. Tell me more.
Why should we be concerned about these findings?
We don’t know why, over the past three decades, fewer baby boys are being born every year in the U.S. and Japan, or why similar patterns have occurred in Canada and some regions of many industrial nations. We think it’s not likely that this drop in male births can be attributed to individuals having children at a later age or that they’re using more drugs or alcohol. Should I be alarmed?
Were you surprised by these results?
The British Medical Journal recently asked if men were in danger of extinction. They note that men die more often and sooner from all 15 leading causes of death than do women. Some trendy magazines even suggested that male health is becoming an oxymoron.
Our new paper shows that the decline in the birth of baby boys has continued in the 1990s. While the percentage drop is very small, (0.022 per 1,000 births over the last 30 years in the U.S.), this translates into huge numbers in the U.S. and Japan. Currently, there are about 4 million births per year in the U.S., so this small number is significant and of public health importance. Give me the details.
Do environmental factors impact mothers and fathers equally?
While the role of mothers is obvious, the impacts that affect the fathers are certainly going to be more important here because the fertilizing sperm determines the sex of an embryo. Male health and reproductive problems.
Why are boys, as opposed to girls, more severely affected by these environmental factors?
The sex of a baby is determined by the sperm. If sperm shape, strength, speed, or structure is damaged prior to the fertilization of the egg, this can throw off-kilter the exquisitely sensitive chain of events that lead to normal reproduction and development.
The difference between a male and female all comes down to a Y chromosome. Males with their XY “sex gene,” as opposed to females with their XX, lack the extra leg on which to stand. The Y chromosome appears to convey some sort of genetic vulnerability that the X does not have. Many diseases disproportionately affect males throughout life. Why?
Isn’t it true that men are facing other reproductive health problems aside from these issues you have described?
Yes. What are they?
Taking this all into consideration, what is the big picture?
All of this is part of a complicated puzzle, but could be part of a larger syndrome of male reproductive health. The same things that are increasing testicular cancer, lowering sperm count and testosterone, could also be involved in reducing the odds that baby boys will be conceived and born. How?
What are some of the sources of these environmental toxins?
One is a persistent chlorinated pesticide called dibromochloropropane (DBCP).
Are mercury and plastics causes for concern, as well?
Mercury, in the United States, comes primarily from seafood. Fish and other varieties of seafood are exposed to mercury from a combination of industrial uses and power plants, which emit mercury when they burn coal. So, burning coal is a problem.
Not all plastics are bad, though some of the wrappings for meats and cheeses are made with polyvinyl chloride, which can be released into the food.
Couldn’t increased psychological stress be the cause of the sex ratio changing?
Stress can do a lot of things, but it's unlikely that with populations of over 400 million people you're going to get stress alone explaining these things. One of the most important clues to all of this comes from research in Sarnia, Ontario, Canada, where a community complained about the lack of boys being born. What happened?
Why is the sex ratio for African-Americans holding more steadily as the whites’ declines?
The short answer is: we don't know. But the fact is, there are proportionally fewer black boys born than white boys in the first place. And the fetal death rate of males, in the year 2000, was more than twice what it was for whites--so perhaps that's accounting for some of this. There are also higher testosterone levels in black women than in white women, and black men do not get testicular cancer at the same rate that white males do. So if we conclude that whatever is causing the rise in testicular cancer is also associated with lower birth rates, you could make the argument that it may not apply to blacks. But at this point, we really don't know.
Are the sex ratios in countries other than Japan and the U.S. following this downward trend?
Tiny amounts of fumes, gases and alcohols hardly seem like strong enough factors to affect a man’s ability to reproduce.
Fat has been called a natural hazardous waste site, because it attracts chlorinated organic materials, whether they are sloshed onto the skin or inhaled into the lung. One of the fattiest remnants of the human body is seminal fluid, which packages sperm and provides a ready vehicle for continued exposure even after pregnancy has begun. What's in it?
What other areas have presented such unusual patterns?
Professor Andrew Watterson of Scotland’s Stirling University reports that for Scotland overall sex ratio has not declined, but within one highly industrialized region of Forth Valley, in Falkirk, some of the lowest sex ratio of births occurred in the most polluted zones in the past twenty years. More.
What about smoking, alcohol drinking, or obesity? Couldn’t they account for these trends?
As to the reported observation that smokers have reduced sex ratio in their children, insofar as smoking rates have DECLINED recently in all industrial countries, this seems a highly unlikely explanation of our findings. As to obesity or drinking, or other such behavioral changes, there is not likely to be one simple explanation for something as exquisitely sensitive as sex ratio. These factors need to be considered along with the increased use of hormone mimicking compounds. Alcohol and obesity both increase estrogens. Obesity results from excess nutrition and inadequate activity, but also can be affected by eating foods or drinking alcohol that contains hormonally active compounds. What does that mean to me?
