Study co-author Ahmed El-Sohemy, a professor of nutrition at the University of Toronto's Faculty of Medicine in Canada, and colleagues recently reported their findings in the Journal of Nutrition.

Lactose intolerance is defined as the body's inability to effectively digest lactose, a sugar found in dairy products, including milk, butter, and cheese.

The condition occurs when the small intestine fails to produce sufficient amounts of lactase, which is the enzyme that breaks down lactose.

If a person with lactose intolerance consumes dairy products, they may experience bloating, flatulence, diarrhea, nausea, and abdominal pain. These symptoms usually arise around 30 minutes to 2 hours after lactose consumption.

It is unclear precisely how many people are living with lactose intolerance, but estimates suggest that around 65 percent of the population experience a reduced ability to digest lactose following infancy.

One cause of lactose intolerance is mutations in the LCT gene, which is the gene responsible for lactase production.
People with lactose intolerance should be aware of vitamin D intake

From an analysis of 1,495 men and women who were a part of the Toronto Nutrigenomics and Health Study, El-Sohemy and colleagues found that people who possessed LCT gene mutations had a lower intake of dairy products, compared with the general population.

Individuals with LCT gene mutations also had lower blood levels of vitamin D, which the team says is likely down to reduced intake of dairy products, since these are often fortified with vitamin D.

"We were not surprised that lactose intolerant people ate less dairy," says El-Sohemy, "but we were surprised that they did not compensate by supplementing or eating other foods fortified with this crucial nutrient."

Vitamin D is considered essential for the absorption of calcium in the gut, which is important for good bone health. The vitamin also aids nerve functioning and helps the body to stave off bacteria and viruses.

Interestingly, the researchers found that people with LCT gene mutations were shorter than individuals in the general population, which indicates that reduced intake of vitamin D through lack of dairy consumption may be inhibiting bone growth.

El-Sohemy and colleagues say that their findings suggest that people with lactose intolerance should consider increasing their intake of vitamin D through non-dairy food sources.

    "These findings speak to the need for greater awareness for those who limit dairy because of lactose intolerance. They need to be mindful of getting enough vitamin D from other fortified foods like certain brands of orange juice, or to consider trying lactose-free dairy products."   Ahmed El-Sohemy

Another finding of the study was that individuals with just one mutated copy of LCT demonstrated an intolerance to lactose, but to lesser degree than those with two mutated copies; it was previously thought that two mutated copies of the gene were required for lactose intolerance to arise.

According to the researchers, this finding indicates that clinical definitions and genetic classifications for lactose intolerance may need to be reviewed.