Drugs called selective serotonin reuptake inhibitors (or SSRIs) is used by up to 30% of pregnant and lactating women to treat depression symptoms. These drugs increase circulating serotonin levels. Non-lactating women, men and children who take SSRIs show signs of increased rates of osteoporosis and have an increased fracture risk. An additional concern for bone health is however created by breastfeeding.

Women who breastfeed exclusively for six months lose somewhere between six and 10 percent of their bone mass in that time. This is due to calcium being relocated to milk. If the mother is taking an SSRI at the same time, that bone loss could be further exacerbated.

Serotonin is probably best known for causing feelings of happiness in the human brain. In a study conducted by scientists at the University of Wisconsin-Madison, it was found that serotonin plays a role in the milk production of dairy cows. This finding may have health implications for breastfeeding women.

When the amount of calcium circulating in cow’s blood decreases, they develop a disease called milk fever. In serious cases, cows get cold and develop noticeable tremors. Milder case of milk fever can still cause inadequate calcium for milk production and health problems for the cows. As many as half of all dairy cows develop the milder version. As you don’t see the animal shaking, this form is not easy to identify. Laura Hernandez, a UW-Madison professor of dairy science notes that the cows also become susceptible to other diseases because of the low calcium associated with milk fever.

In a new study conducted on both Jersey and Holstein cows, it was found that increased serotonin levels lead to increased calcium levels. What was unexpected is that the increase in calcium levels happened in different places in the different dairy cow breeds. The cows were injected with a compound that is metabolized into serotonin.

Hernandez observed that in the Holsteins, an increase in calcium was detected in the blood, while in the Jersey cows, serotonin increased calcium in the milk. The team was able to see that the calcium regulation is different because they looked at both breeds. The next step to translating these findings into treatments for milk fever is to understand how the calcium regulation works on a molecular level.

Although the objective of the research is healthier cows, understanding the relationship between serotonin and calcium may also help improve breastfeeding women’s health. The team’s work suggests that the higher levels of serotonin would increase circulating calcium that would otherwise be used to strengthen bones. In humans, this causes concern about bone loss.

This is a classic case of how research on a different disease in another species could help to explain bone loss in humans and uncover possible treatments. Understanding the basic science would help both sides. Once the molecular mechanisms are understood on a biological level, there would likely be ways the system can be manipulated to improve both human and cow health.

Study was published in the Journal of Endocrinology.