What are the future research needs for understanding and managing lactose intolerance?
Reliable estimates of the U.S. prevalence of lactose intolerance and lactose malabsorption are not available in a representative population of diverse ages and races/ethnicities. Most of the available research assessed subjective symptoms in an unblinded fashion in selected groups of subjects or in individuals unable to fully absorb lactose irrespective of symptoms of lactase nonpersistence. Therefore, we recommend that a study be conducted to determine the prevalence of lactose intolerance in the U.S. population and the differences across age and racial/ethnic groups. The study should examine a representative sample of the U.S. population and determine the following:
• The prevalence of self-reported baseline symptoms
• The prevalence of lactose malabsorption with or without symptoms following a blinded lactose challenge
• The relationship between self-reported symptoms and the presence of lactose malabsorption
• The prevalence of lactose intolerance in those individuals with lactose malabsorption based on the blinded challenge.
The best approach to minimize placebo effects is to conduct blinded challenges using a standardized, taste-masked dose with and without lactose and to define symptoms using a well validated scoring system. Studies on what constitutes an optimal challenge dose of lactose also should be conducted. Dietary history regarding lactose consumption and symptoms associated with polymorphisms affecting lactase gene expression potentially could obviate the need for taste-masked, blinded oral challenges with lactose and placebo. An opportunity exists to use the infrastructure of the ongoing National Health and Nutrition Examination Survey or other ongoing nationally representative studies, which already are collecting dietary intake data and would allow additional and potentially informative evaluation of the intake of lactose-containing foods in those with rigorously determined lactose malabsorption with or without symptoms.
Despite the widespread belief that decreased vitamin D and calcium intake associated with restricted intake of dairy products will lead to poor health outcomes, particularly related to bone mineral density and risk for fractures, few data are available on bone health in individuals with lactose intolerance and dairy avoidance. Future studies should investigate the association between dietary calcium intake and outcomes in people with lactose intolerance on low-lactose diets. A diverse population should be evaluated including children, the elderly, males and females, members of ethnic/racial subgroups, and those with susceptible genetic polymorphisms. The latter genetic alterations should include potential modifying genes. Also, the efficacy of dietary calcium intake from nondairy products and from nutritional supplements should be examined in relation to bone health and as to whether other foods influence calcium absorption from these sources.
Although puberty is the period of most rapid accrual of bone mineral, studies are needed to determine whether calcium intake during this period will affect the subsequent risk to develop osteoporosis. Other health outcomes including obesity, diabetes, cardiovascular disease, and cancer also should be assessed in individuals with treated and untreated lactose intolerance and in other individuals avoiding milk products because of perceived lactose intolerance in comparison with the general population. Additional issues of importance need to be addressed in children with lactose intolerance through long-term observational studies and randomized controlled clinical trials of various treatment strategies. These issues include the incidence of infection, allergic disease, and standard measures of growth and development.
Data are lacking as to whether individuals of different races/ethnicities, ages, and genders who have lactose malabsorption have differing tolerance to lactose. Blinded, randomized controlled trials are needed to determine if the quantity of lactose that can be tolerated by lactose-intolerant individuals varies by race, ethnicity, age or gender. Symptoms should be reported in a standardized, validated format so that clinically important differences can be appreciated.
The lack of uniformity in study design and methodology hampers a rational, evidence-based approach to management of lactose intolerance. Defining the tolerable dose of lactose in those with lactose malabsorption is critical to determining the clinical importance of lactose malabsorption and the prevalence of lactose intolerance, and it may provide critical information for management. A stepwise approach should be developed to define the specific amount of dairy foods to introduce to the individual with lactose intolerance (i.e., the greatest amount of lactose that is not associated with symptoms). Studies also should be conducted to confirm whether lactose is better tolerated if distributed throughout the day or given with meals. Some individuals have reported moderate value in reducing symptoms by using lactase or lactose-hydrolyzed milk; however, sample sizes and the reporting of symptoms were so variable in reported studies that making firm recommendations is difficult. The use of prebiotics (a nondigestible food component, usually a carbohydrate, which benefits the recipient by promoting intestinal colonization by beneficial bacteria) and probiotics in dietary supplements and foods including yogurt is a popular intervention for individuals with lactose intolerance, but further studies are needed to document the efficacy of such products in reducing symptoms. Calcium intake from low-lactose dairy products, nondairy products, and nutritional supplements is an alternative management strategy in individuals with lactose intolerance, but few data are available on the effect of such interventions on individual outcomes, including bone mineral content and fractures.
It will be important to determine whether testing for lactose malabsorption will change the behavior of individuals who avoid dairy products, many of whom may not have lactose intolerance. Future research should employ standardized interventions, blinded controls, and reporting of improvement of symptoms in a consistent, validated fashion to compare the efficacy of these dietary management strategies in obtaining clinically meaningful health outcomes.
Once effective interventions have been identified, behavioral and culturally sensitive approaches to convince people to adopt recommended dietary changes should be developed and tested. Clearly, the perception of symptoms in individuals with lactose intolerance may be highly subjective and very susceptible to a number of psychological and cultural factors. Thus, various strategies may result in very different behavioral changes, and their effectiveness should be compared rigorously.
Additional work needs to be done to improve the management of patients with irritable bowel syndrome and a hypersensitive colon who also may have lactose intolerance.
The Lactose Intolerance Clearinghouse Has Moved.
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