The mystery surrounding a mummified toddler has been solved four centuries after his death, thanks to what scientists call a “virtual autopsy.” And they think he died of an issue that has gotten much attention in recent years. Doctors have warned about it, and they’ve urged daily action to prevent it, particularly during the COVID-19 epidemic.

The child was found in Hellmonsödt, Austria, in a wooden coffin inside a crypt for the Counts of Starhemberg. It belonged to an upper-class family of the 17th century, one of the oldest aristocratic families in the country. Researchers from Germany’s Academic Clinic Munich-Bogenhausen determined that the boy was likely Reichard Wilhelm, who died in 1625 or 1626.

The crypt contained several members of the family. All of them were buried in ornate metal coffins—except for the toddler, whose simple wood casket was unmarked. What led to the child’s demise at such a young age? Read on to find out what the scientists discovered.

According to the study, published this week in the journal Frontiers in Medicine, the boy’s body was well-preserved and had become mummified, allowing researchers to analyze its soft tissue. To do this, they used a CT scanner.

Meanwhile, radiocarbon dating allowed scientists to pinpoint when he had lived. “According to our data, the infant was most probably [the count’s] firstborn son after erection of the family crypt, so special care may have been applied,” said Andreas Nerlich, the study’s lead author.

The research team studied the child’s teeth and measured his bones, which indicated he was between 12 months and 18 months old when he died. The boy had dark hair and was overweight for his age, suggesting he was well-fed.

However, the CT scan revealed that his ribs were deformed, indicating a metabolic bone disease. They had developed in a pattern called a “rachitic rosary,” a condition in which knobs of bone develop at the junction of ribs and cartilage. It’s usually seen in severe cases of rickets or scurvy. The scan also revealed inflammation of the lungs characteristic of pneumonia.

To the researchers, this indicated that although the toddler had been fed enough to put on plenty of weight, he was still malnourished. They suggest he developed a vitamin D deficiency after being kept inside and away from sunlight.

Rickets is primarily caused by a deficiency of vitamin C, and a vitamin D deficiency has been associated with several serious illnesses, including respiratory diseases. The scientists concluded that the child had died of pneumonia, and his nutritional deficiency may have been a contributing factor.

The scientists noted that in the 17th century, members of the upper class avoided sunlight. Pale skin was considered desirable and a mark of wealth—only laborers developed tans from toiling in the sun.

“The combination of obesity along with a severe vitamin deficiency can only be explained by a generally ‘good’ nutritional status along with an almost complete lack of sunlight exposure,” said Nerlich. “We have to reconsider the living conditions of high aristocratic infants of previous populations.”