Lactose Intolerance

by Richard Mitchell, MD, PhD

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    00:01 Welcome.

    00:02 In this talk, we're going to deal with lactose intolerance.

    00:06 Mooo...

    00:08 So lactose intolerance is a constellation of symptoms that are due to a lactase deficiency.

    00:14 Within the small bowel, you're lacking an enzyme that's going to be responsible for breaking down that sugar, which is found in a high concentration within milk and other dairy products.

    00:26 The epidemiology of this.

    00:29 So in children, there's a very low prevalence.

    00:31 Most kids do just fine.

    00:34 They have adequate lactase expression, certainly until they get to 6 or even into their teenage and young adult years.

    00:42 In adults, however, a greater than 70%.

    00:45 So almost three quarters of adults have a primary lactase deficiency.

    00:49 Now, they're not going to be lactose intolerant, necessarily.

    00:53 So about less than half will actually not be able to drink milk, they just may not be able to get the maximum benefit out of it, and may have some symptoms related to drinking liquids that have lactose within them.

    01:10 In adults, the lowest prevalence for lactase deficiency or lactose intolerance is in Northern Europeans.

    01:16 It's actually much, much more common in populations with African, Asian, Hispanic and Native American heritage.

    01:24 The pathophysiology is pretty straightforward.

    01:26 It has to do with an enzyme deficiency in breaking down the lactose.

    01:31 So in most adults, as you get older, you tend to lose that enzymatic expression.

    01:39 There's a genetic variability and clearly in Northern European populations, you tend to preserve expression much more commonly.

    01:46 In other populations, you tend to lose it much more commonly, and it's an age related decrease in the lactase expression.

    01:53 There may be other secondary causes.

    01:55 So not just a primary age related loss of expression, but certain infections or mucosal disease such as celiac disease, or chemotherapy can cause loss of epithelial enzyme expression, or even loss of epithelial surface area, which can give manifestations similar to lactase deficiency.

    02:18 Let's look at this on this schematic.

    02:21 So you have in the small intestine, you have various compounds that have been ingested, In this case, we're talking about lactose and lactose is actually a sugar of glucose and galactose.

    02:34 It is a dimer that needs to be degraded before the individual sugars can be absorbed.

    02:42 Lactase would normally break them down into galactose and glucose which can be independently absorbed.

    02:48 But we don't have transporter proteins for lactose, the nondegraded sugar that's why you need to have lactase.

    02:57 In that setting, we're good to go.

    02:59 We've absorbed galactose and glucose, whom can use that for energy and for building blocks, etc.

    03:05 In the setting where you don't have any lactase, now that lactose doesn't get broken down, it can't be absorbed, it's going to have an osmotic effect, it's going to suck in water.

    03:16 So that will obviously increase diarrhea, but also it's going to be a really great substrate for bacterial fermentation more distally.

    03:26 So now the bacteria are gonna go 'yum', you've given us sugar that we can degrade.

    03:31 And as they degrade that that fermentation leads to production of hydrogen gas and carbon dioxide.

    03:38 It also produces methane or produce lactic acid, and acetic acid, and all of those things create again, an increased diuresis or absorption of water because of all the solutes that are in there.

    03:54 And we end up with loose stools, we have much more gas, so there's bloating and flatulence, and with the expansion due to the gases, there will be abdominal pain.

    04:06 So the clinical presentation.

    04:07 Pretty straightforward once you understand the pathophysiology.

    04:11 The poor unfortunate patient with lactose intolerance, who is now had a big bolus of lactose will have diarrhea, and there will be bulky frothy and watery stools due to the fermentation of that lactose by bacteria further down in the bowel.

    04:27 You may actually have with that increased diarrhea, poor absorption of all the other nutrients, so you may experience weight loss.

    04:36 There clearly be abdominal pain because the gas will distend the bowel and it will hurt.

    04:41 And there will be a sense of bloating, again, associated with the fermentation and the gas accumulation.

    04:48 And when the gas comes out, flatulence.

    04:51 Nausea because dilation of the bowel does cause you to feel sick to your stomach and you may have frank vomiting.

    04:58 Making the diagnosis is usually kind of cause and effect.

    05:02 When you have milk, you have symptoms.

    05:05 So it's a clinical diagnosis.

    05:06 And we can do however other formal testing.

    05:10 One is a lactose hydrogen breath test.

    05:12 So we will administer lactose.

    05:15 And normally, we don't, our own GI tract won't make significant amounts of hydrogen.

    05:23 However, if you have a lactase deficiency, that lactose bolus will lead to a lot of hydrogen formation that can be detected in the breath.

    05:33 So you get absorption into the vasculature and then you breathe it out.

    05:40 Some clinicians will also look specifically for methane.

    05:43 And because you may get other forms of fermentation depending on the microbiota.

    05:49 In some cases, you may do a small bowel biopsy to make sure that there is not celiac disease or some other entity that's causing this lactose intolerance.

    05:59 Again, just speaking to the other secondary causes of lactose deficiency or lactase deficiency, are infectious enteritis can include giardia and other things, celiac disease, so gluten sensitive and neuropathy, inflammatory bowel disease, and certainly certain drugs and radiation induced enteritis will do this as well.

    06:18 The management.

    06:19 Well just get rid of the milk.

    06:21 Okay, do lactose restriction.

    06:24 We can also substitute other forms of milk, so soy milk or other vegan alternatives.

    06:32 You can concurrently with the ingestion of lactose have lactase enzyme preparations that will enzymatically break down the lactose before it gets to the point where the bacteria will use it for fermentation.

    06:46 And clearly, if you're not drinking or having as many dairy products, you do need to increase your consumption of important nutrients that are present in milk such as calcium and vitamin D.

    06:58 If it's a secondary cause, if it's celiac disease, or it's radiation induced enteritis or other things of that nature, you treat that primary disorder.

    07:08 With that, we've reached the end of lactase deficiency or lactose intolerance.

    About the Lecture

    The lecture Lactose Intolerance by Richard Mitchell, MD, PhD is from the course Small and Large Intestines Disorders.

    Included Quiz Questions

    1. Lactase deficiency
    2. Lactase overgrowth
    3. Lactase stasis
    4. HLA DR4-DQ8 mutation
    5. HLA DR2-DQ8 mutation
    1. Northern Europeans
    2. Africans
    3. Asians
    4. Central Americans
    5. Native Americans
    1. Psoriasis
    2. Infectious enteritis
    3. Celiac disease
    4. Inflammatory bowel disease
    5. Drug-induced enteritis

    Author of lecture Lactose Intolerance

     Richard Mitchell, MD, PhD

    Richard Mitchell, MD, PhD

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