For Years, Scientists Have Been Leaving Out One Crucial Thing From Their Experiments

The news: Lack of female representation in STEM fields is a well-known fact — but who knew that gender imbalance extended to mice as well?

The National Institute of Health published an article Thursday in the journal Nature, warning researchers to be more mindful when selecting lab specimen. The reason: There is a huge sex gap among lab mice. One survey of 1,200 neuroscience papers found that only 42% of reported the sex of the animals used ,and of those, only 24% included female animals in their study. 

"The over-reliance on male animals and cells in preclinical research obscures key sex differences that could guide clinical studies," the article said. While some researchers said they were concerned about female mice's reproductive cycles and hormonal fluctuations, others said they were simply sticking with the status quo — revealing a glaring blind spot in the earliest stages of research.

The NIH is now introducing a requirement for researchers seeking a grant from the agency: Applicants must provide plans for balancing male and female animals in lab studies, as well as cells and tissues from different sex. Given that the NIH gives out $30 billion in funding every year, this is a huge step for the biomedical research community — and a long overdue one to correct gender bias in science.

Why this is important: Gender imbalance among mice might sound like a frivolous problem, but it actually has huge repercussions for people. Male and female bodies can have vastly different reactions to a certain drug or treatment, and underrepresenting a sex in a laboratory setting can allow researchers to overlook dangerous side effects.

"Every cell has a sex. Each cell is either male or female, and that genetic difference results in different biochemical processes within those cells," said Janine A. Clayton, a NIH director who co-wrote the article. "If you don't know that and put all of the cells together, you're missing out, and you may also be misinterpreting your data."

And the negative impact of this gender disparity is very real.

"Name a new drug or treatment, and odds are researchers know far more about its effect on men than on women. From sleeping pills to statins, women have been blindsided by side effects and dosage miscalculations that were not discovered until after the product hit the market," the New York Times writes.

It's simple science: You need a wide, diverse sample group in order to get comprehensive results. Back in 1994, the NIH took a huge step by pushing for the inclusion of women and minorities in clinical studies; now the agency is acknowledging that gender imbalance begins at a much earlier stage of research and that ignoring the problem is not only unethical — it's just lazy.