Absorbing calcium

Although the cause of hypercalcemia is a mystery 1in Williams syndrome, we do know a little about how the calcium is absorbed in the gut. Many people think that the stomach is the main area of digestion in your body. Although it does digest proteins, the majority of the food is broken down and absorbed by the small intestine. The lining inside of your small intestine is a network of finger-like bumps that are filled with blood vessels and covered by a very thin layer of skin that sits between the vessels and the food/enzyme mixture in your gut.




Most calcium in your small intestine is absorbed in the lower regions called the ileum and jejunum. These are the main portions of your intestine that absorb nutrients and minerals. Calcium here will move passively into the blood stream. This means that it can easily slip through little spaces in the skin layer (called the epithelium) and into the blood. If your diet provides your body with enough calcium, this is the main type of transport you'll use.




If calcium levels are low, your body has to work a little harder to get the amount it needs. This is where vitamin D comes in. Vitamin D operates channels that collect calcium in the upper third of the small intestine, called the duodenum. These channels are activated when vitamin D binds to proteins in the epithelium (skin) layer. These proteins work with active transport, where the body uses energy to pump the calcium into the blood stream, increasing its levels in the blood. This is why, if you increase the vitamin D in your diet, you end up increasing the calcium in your blood stream.




This vitamin D metabolism is one of three theories I could find that try to explain infantile hypercalcemia in WS. Researchers have found that when children with hypercalcemia are managing their calcium levels and only slightly rise the vitamin D in their diet, their calcium levels increase dramatically. They found that by only making small increases in vitamin D, children with WS absorb 2-3 times more calcium than what would be expected in a typical child.




Another factor that influences calcium absorption is the type of food you eat. If you are a milk drinker, you're going to have more passive calcium absorption- the easy kind in the lower intestine. Milk contains sugars called lactose and an enzyme called lactase both of which help the body collect the calcium and absorb it into the blood stream. Other foods also contain calcium, such as spinach. Foods that are high in fiber and contain calcium tend to be harder for your body to digest. The fiber, called oxalate, binds to the calcium and holds on to it as it passes through the gut. Therefore, if your primary calcium sources are in high fiber foods, you will essentially absorb less of them and excrete more due to the food's chemical nature.







Oxalate has other affects on your body, too. If the level of calcium is low, your body will start to absorb more oxalate instead of excreting it. Essentially, if you are in a pinch for calcium, you'll take what you can get even if it's in a form that you don't really prefer. The increase in oxalate signals the kidneys to work harder to get rid of it. Calcium oxalate then builds up in the kidneys and can cause stones, or nephrocalcinosis (see the growth and diet page on this blog). This is why some doctors will place a child with hypercalcemia on a low oxalate diet- to prevent the uptake of calcium and reduce dangers of developing kidney stones.



It's important to note that although many WS infants with hypercalcemia have higher than normal levels of vitamin D, there are exceptions to the rule. There is a significant population of individuals who have high levels of calcium and LOW levels of vitamin D. Since most foods contain both, this can create quite the dilemma to try and maintain proper levels of each. Stay tuned for future blog posts discussing this topic and other theories of why our little ones have hypercalcemia!

WS- a major player in what we "know" about vitamin D

Over the past couple of days I've had a couple of parents send me questions about calcium and vitamin D and how they affect WS. Those questions will be answered in future blog posts but until then, I found some interesting information about how WS has changed the way many researchers have viewed vitamin D. I've enjoyed getting questions from other parents because I've learned so much in the quest to answer them! Keep them coming :)



Although this is a science-based blog, here is your history lesson for the day:

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  In the 1960's it was thought that supravalvular aortic stenosis (the characteristic heart defect of WS) was caused by the mother ingesting too much vitamin D during pregnancy. At the time, researchers didn't know about Williams syndrome and its genetic component. A study performed in the late 1950's drew a connection between SVAS and hypercalcemia (or high calcium in the blood). WS is the only identified disorder that has unexplained hypercalcemia before the age of 1. So, the researchers put two and two together and concluded that high levels of vitamin D lead to heart defects and all the symptoms of what we today know as Williams syndrome- SVAS, low IQ, and hypercalcemia. The study started a Vitamin D scare that changed the Food and Nutrition Board recommended values for Vitamin D to lower levels in Britain and the US. Until the 1980's when genetics identified that SVAS is due to a genetic defect did the vitamin D theory change.

Recently, a new vitamin D theory has surfaced and again, it's basic idea is based on what else, Williams syndrome:

• A group of researchers began in 2007, studying a link between vitamin D deficiencies with the increase of autistic children. The researchers studying this connection are using Williams syndrome as the basis of their hypothesis. Their reasoning is that the highly sociable personalities of WS are opposite those of autistic children. They think that social behavior is directly related to vitamin D levels- WS, having high levels of calcium and vitamin D in the first year of life leads to high social nature versus autism that could potentially have low levels of vitamin D and exhibiting anti-social behaviors. Their hypothesis is that vitamin D levels in the body determine the social nature of each disorder.

They don't comment on the fact that some kids with WS are also autistic, making me skeptical, but still an interesting study! It just goes to show you, what you "know" today may not be considered right in the future. And that my friends, is what makes science so interesting to me. There is always more to learn.