Why are adults lactose intolerant?

Lactose intolerance (or hypolactasia) is the term used to describe a decline in the level of lactase, an enzyme needed for proper metabolization of lactose (a sugar that is a constituent of milk and other dairy products), in human beings. An estimated 70%[1] of adult humans are considered lactose intolerant and therefore, from a world view, lactose intolerance can be regarded as "normal" for adult humans whereas lactose tolerance may be considered a form of neoteny.

There are three major types of lactose intolerance[2]:

Primary lactose intolerance. Environmentally induced when weaning a child in non dairy consuming societies[3]. This includes many Asian and African cultures, where industrialized and commercial dairy is uncommon.

Secondary lactose intolerance. Environmentally induced, resulting from certain gastrointestinal diseases, including exposure to intestinal parasites such as giardia[4][5]. In such cases the production of lactase may be permanently disrupted.[7] + (Wiser 2000, Pennardt 2006). A very common cause of temporary lactose intolerance is gastroenteritis, particularly when the gastroenteritis is caused by rotavirus.

Congenital lactase deficiency. A genetic disorder which prevents enzymatic production of lactase. Present at birth, and diagnosed in early infancy.

You can become lactose intolerant as an adult. I did, and my husband did, although mine is more severe. His grandfather and my grandmother were both lactose intolerant, and both became so later in life. You might consider going to rice milk, soy milk (such as silk) or goat's milk. I am not big on rice milk and I am also allergic to soy so I drink goat's milk, eat goat"s milk yogurt and use goat's milk butter. All of the pain has gone away since I switched. Try cutting it out for a few days. Then have a glass of milk and see what happens! When you think about it, humans are the only animals that drink milk after we are weaned, and we don't even drink human milk...we drink the milk of another animal!

If you believe in evolution (and I can't understand why people can't!) then the answer lies in your genes. Scientists have found a single gene which is responsible for lactose intolerance. Basically, a few thousand years ago one of our genes mutated and this produced the code for the enzyme responsible for breakdown lactose in milk produce. Most of the world now has this gene and can drink milk just fine.

However, some people still do not have that gene, or it has mutated such that they still cannot digest milk (like cats - cats are also lactose intolerant, you should never feed them normal milk). This is a good example of 'negative' evolution, it doesn't harm you by not having the gene, so it will never really get phased out.

The only way for anyone to not become lactose intolerant is to never stop drinking milk once you start (from childhood). Nothign you can do about it now, unfortunately.

I am not lactose intolerant yet almost 40

You can be lactose intolerant at any age.

they're born that way i believe. my 10 year old cousin has always been lactose intolerant

Because they don't have enough lactase which is the enzyme used by the body to process lactose, the sugar in dairy products.

they were born with lactose intolerant and they can't help it

go to http://www.notmilk.com/

you'll find the best answer/s to your question/s regarding lactose intolerance and more...