In 1928, Lucy Wills was recruited to India and tasked to investigate why millions of pregnant women in the developing world suffered from a severe and often deadly form of anemia.

She found the red blood cells of anemic pregnant women were extremely swollen and consequently not carrying enough hemoglobin. Wills first thought that a bacteria or virus might have caused anemia. But she noticed that richer women in India who had a more nutritious diet were less likely to become anemic during pregnancy.

• Wills decided to feed rhesus monkeys in a laboratory with a diet similar to the anemic women. Many of the monkeys came down with anemia.
• Wills found that liver extract, a previous remedy that was effective in treating Addisonian anemia, was an effective treatment of the type of anemia Wills was researching. However, she needed a very high dose to combat anemia in pregnant monkeys.
• Liver extract was expensive at that time, and thus not a suitable solution.
• Wills found that Marmite, a cheap bread spread made from concentrated brewer's yeast, was very successful in treating anemic monkeys.
• Turning to anemic pregnant women, she found an increase in the red cell count by the fourth day but admitted that she didn't know which compound in the Marmite and liver extract was responsible for the cure.

In 1941, the "Wills Factor" was isolated as folic acid. Since the discovery, folic acid has also been found to reduce the risk of severe birth defects, known as neural tube defects that lead to permanent disability, damage to the skull or brain, and often early death.