Clinical Research on Lactose Intolerance
National Institutes of Health (NIH) Report on Lactose Intolerance
June 15th, 2011
The National Institutes of Health (NIH) Consensus Development Program has been organizing major conferences since 1977. The program generates evidence-based consensus statements addressing controversial issues important to healthcare providers, policymakers, patients, researchers, and the general public. In 2010, the Consensus Development Program held a conference covering lactose intolerance and health. Linked below are both the final panel statement and evidence report on their findings.
Steve Hertzler, PhD, RD- The Latest Clinical Research Findings:
Monday, November 19th, 2007
I am a professor of human nutrition at Iowa State University. I did my PhD work in the area of lactose intolerance and have published many research and review articles on this topic. My focus was on colonic bacterial adaptation to lactose. There is some relatively new information on the diagnosis of lactose intolerance that I think should be included in this blog.
First, it is very important that people do not “self-diagnose”. In addition, even when an individual goes to a physician for a diagnosis, the physician often uses an incorrect approach. The classic example of this is to put the patient on a lactose-free diet and see if the symptoms go away. The potential for “placebo” effect in this type of diagnosis is enormous. From double-blind studies our laboratory group conducted at the University of Minnesota, 1 out of 3 people who “self-diagnosed” themselves as severely lactose intolerant were actually able to digest 15 g lactose (just over 1 cup of milk). It is important to have objective evidence of lactose maldigestion. It is also important to realize that lactose maldigestion among varying individuals is more of a continuum than an “either-or” phenomenon. For example, traditional lactose tolerance tests done by physicians used 50 g of lactose in water after an overnight fast. This is equivalent to drinking a quart of milk on an empty stomach! This is not very physiological or realistic. Just because a person can not tolerate 50 g does not mean that he/she won’t tolerate the 12 g in a cup of milk. In our double-blind studies, the symptom response to 12 g lactose was about 25% of subjects, which was not statistically different from a lactose-free placebo. Dose of lactose is a very important factor.
How should lactose intolerance be diagnosed? First, there is a difference between lactose maldigestion and lactose intolerance. The former term means that a person is unable to digest lactose to a certain degree. On average, lactose maldigesters malabsorbed about half of the lactose in 1 cup of milk (some more, some less). However, not everyone experiences symptoms from lactose maldigestion. I once did breath hydrogen testing on a dietitian who worked for the National Dairy Council. She turned out to be a lactose maldigester, but she had no symptoms from drinking milk. Lactose intolerance is when lactose maldigestion is coupled with gastrointestinal symptoms such as diarrhea, flatulence (most common), and stomach discomfort. A person who is experiencing GI symptoms that he/she suspects might be related to lactose maldigestion needs to have confirmation by an objective test. This is important to rule out other potential bowel conditions. Irritable bowel can often masquerade as lactose intolerance.
The current diagnostic test of choice is the breath hydrogen/methane test. I perform these tests routinely in my laboratory. The principle of the test is that the fermentation of carbohydrates by the colonic bacteria is the only source of molecular hydrogen in the body. During this fermentation, hydrogen gas is produced and a portion of the gas diffuses from the colon to the blood, with ultimate pulmonary excretion. Thus, if a person has a rise in breath hydrogen following milk consumption that is significantly above the fasting level (around 10-20 ppm), this is objective evidence of lactose maldigestion. The test needs to be performed carefully and it is not perfect all of the time, but it has very high sensitivity and specificity when it is done correctly. It does involve some fasting, but there are no needles and it is totally noninvasive. For research purposes, this test is sometimes paired with other measurements (e.g., urinary/blood galactose in the lactose tolerance test with ethanol), but the standard breath hydrogen test with concurrent measurement of methane works fine most of the time. A dose of lactose that is more physiological (e.g., 12-25 g) is more appropriate than the traditional 50 g test that has been used. Please contact me if you want more information about this.
In addition, there are new genetic tests that are presently being studied. They identify a couple of gene mutations (C/T-13910 and G/A-22018) in the lactase gene that are highly associated with biochemical evidence of lactose maldigestion. Perhaps this could lead to the wide availability of a simple blood test to identify lactose maldigestion. However, this somewhat controversial, as one study has shown that this genetic test that has been effective in some Finnish families was not effective in an African population.
Disclaimer: No medical doctor has reviewed the contents of this website/ blog. This website/blog was development for the purpose of providing a central place for lactose intolerant individuals to come to share basic information and personal insight. It is advised that you check with your physician or medical advisor before acting upon anything learned from this site.