Lactose Intolerance Lactose Intolerance Is the Inability to Digest a Sugar Called

Lactose Intolerance
Lactose intolerance is the inability to digest a sugar called lactose in milk and other dairy products. Adults in most of the world are lactose intolerant, although infants are not. This is because many adults lack an enzyme known as lactase. Lactase, which can be found in cells in the intestine, is the enzyme that breaks down lactose.
Many individuals lose the ability to synthesize lactase after age six. However, not everyone does. Whether or not the body continues to produce lactase often depends on ethnicity. While only 5-15% of adults of European descent cannot digest lactose, 80-90% of adults of African and Asian descent are lactose intolerant. Research has shown that people of northern European ancestry contain a genetic mutation that allows the secretion of lactase in adulthood.
The main symptom of lactose intolerance is gastrointestinal upset. Lactose intolerant people may experience diarrhea, bloating, abdominal pain, gas, and vomiting after consuming lactose-containing foods and beverages. Although there has been some research into gene therapy as a treatment for lactose intolerance, the current best treatment is either ingesting lactase supplements when consuming dairy products or simply avoiding foods containing lactose altogether.
Question: What is the meaning of the word synthesize in the passage?

A) Eat
B) Assume
C) Digest
D) Produce