Lactose Intolerance and Its Connection to Low 25-Hydroxyvitamin D Levels

Study Reveals Genetic Link Between Lactose Intolerance and Vitamin D Levels

Findings on Genetic Variants

A recent study has identified a genetic variant in a DNA region upstream of the human LCT gene associated with lactose intolerance. This variant is notably less common in Caucasian populations and more prevalent among East Asian groups. The research also establishes a connection between lactose intolerance and lower levels of 25-hydroxyvitamin D (25(OH)D), indicating that lactose-intolerant individuals face a 2.5-fold higher risk of insufficient or inadequate 25(OH)D levels.

Understanding Lactose Intolerance

Lactose intolerance occurs when individuals are unable to properly digest lactose, the primary sugar found in milk. This condition can lead to various discomforting symptoms, including gas, bloating, abdominal pain, and diarrhea. The root cause is a deficiency of lactase, an enzyme produced by the brush border cells in the intestine, essential for breaking down lactose. Most infants produce sufficient lactase, but its production typically declines between the ages of 2 and 12 years, influenced by genetic factors. A significant percentage of individuals of African, Asian, or Hispanic descent experience lower lactase levels, and this condition is also observed in people of Mediterranean heritage. Conversely, lactase production generally persists into adulthood for those of north European descent.

The Genetic Mechanism

The LCT gene, which encodes for lactase, is regulated by a specific stretch of DNA located upstream. In lactose-intolerant individuals, a single DNA base at a position 13910 bases upstream of the LCT gene is identified as cytosine (C) on both the maternal and paternal chromosomes, known as the CC genotype. In contrast, lactose-tolerant individuals may possess either a cytosine and thymine (CT) combination or two thymine (TT) bases.

Study Demographics and Methodology

It is estimated that approximately 65% of the global population carries a lactose-intolerant genotype. However, the prevalence of this genotype among different Canadian ethnic groups remained unknown until this study, published in the Journal of Nutrition. The research focused on a cross-sectional group of 1,495 Toronto-based participants aged 20-29 years, comprising Caucasian (720), East Asian (506), and South Asian (160) individuals, with other ethnicities making up about 7% of the sample.

Participants provided information regarding their ethnicity, overall health, lifestyle, dietary habits—including dairy consumption—and physical activity through a questionnaire. Fasting blood samples were collected to assess genotypes and levels of circulating 25(OH)D. The study specifically analyzed the Caucasian group for associations between dairy intake and blood 25(OH)D concentrations across the three genotypes (CC, CT, TT).

Study Results

Among the Caucasian participants, 32% exhibited the lactose-intolerant CC genotype. In contrast, this genotype was found in 99% of the East Asian group, 74% of the South Asian group, and 59% of other ethnicities. Notably, the East Asian group demonstrated the highest prevalence of lactose intolerance. The findings indicated that lactose intolerance was linked to a twofold increased risk of insufficient or inadequate blood 25(OH)D levels. Individuals with the CT genotype showed a 50% higher likelihood of having low 25(OH)D levels, suggesting they might also experience the symptoms of lactose intolerance, impacting their ability to consume vitamin D-fortified dairy products.

Limitations and Public Health Implications

One significant limitation of the study was that the analysis linking the three LCT genotypes to 25(OH)D levels was restricted to the Caucasian group, which may limit the applicability of the results to other populations. Additionally, the cross-sectional design means that the participants may not accurately represent the broader population.

Overall, this study highlights a connection between lactose intolerance and reduced levels of 25-hydroxyvitamin D. It underscores the need for individuals with lactose intolerance to ensure adequate vitamin D intake from non-dairy sources. From a public health perspective, the findings suggest the necessity of fortifying non-dairy foods with vitamin D to support those affected by lactose intolerance.

Written By: Usha B. Nair, Ph.D.