The problem, it was eventually found by Wills, was a lack of folic acid – which is now recommended to mothers around the world. But that discovery was neither simple or obvious, and came through a kind of happy accident.

The discovery soon after Wills completed a medical degree. She was educated at a whole host of pioneering institutions: the Cheltenham College for Young Ladies, Newnham College in Cambridge and the London School of Medicine for Women, each of them leading in their field in training women in the sciences.

Following that scholarship, she headed to India, hoping to try and understand a problem that was afflicting a troubling number of women. They were reporting a form of anemia that threatened their lives, and no cause was obvious.

She searched through their living situations and examined their stools, hunting for the cause of the medical problems that were afflicting them. But nothing could be found.

Then she began to suspect that the problem may be their diets. The women were eating an unhealthy and deficient diet, and the anemia seemed to be affecting those with the worst diets the most.

In an attempt to solve that problem, Wills stumbled on an unusual experimental method. She fed a monkey, who until then had been eating a diet similar to the Indian women's, with marmite – and found that it seemed to work, improving the monkey's health.

Marmite was chosen because it was an easy and cheap way of getting hold of yeast extracts, which Wills suspected might improve the women's health.

Work then began to find out what part of marmite was actually improving the health of the women. Some time later, researchers were able to get folic acid out of spinach, finding that seemed to be the important ingredient.

To this day, folic acid is recommended to pregnant women to improve their health. It helps not only with anemia but with other birth defects.

The Independent

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