On pages 50-51 Dr. Moalem talks about vitamin D. This vitamin is essential to maintaining healthy bones and blood. But too little increases the chances of developing diabetes, heart disease, arthritis and certain cancers. Dr. Moalem then explains the relationship between vitamin D and cholesterol, but he doesn't get into detail on how vitamin D is made. Relating to Big Idea 2, how does the body convert cholesterol into vitamin D and how does vitamin D maintain homeostasis within the body? What happens to cholesterol if it doesn't get used? Please discuss the implications of having too much cholesterol in the body as well.
In order to obtain vitamin D, we need to be exposed to ultraviolet B light. As exposure to ultraviolet light increases the more vitamin D we make, but U.V. light also destroys folic acid (page 51). Folic acid is needed to help replicate DNA when the cell goes into the S phase of the cell cycle. So what is the cut off of how much sunlight we need in order to obtain enough vitamin D but also keep supplies of folic acid steady? Is it better to have less folic acid or less vitamin D?
Anna Podber (apodber3@students.d125.org)
“How does the body convert cholesterol into vitamin D and how does vitamin D maintain homeostasis within the body? What happens to cholesterol if it doesn't get used?”
ReplyDeleteProvitamin D3 is photolyzed by UV light to previtamin D3, which isomerizes to vitamin D3. The hormonal (activated) form of vitamin D3 performs calcium absorption, phosphate absorption in the intestine, calcium mobilization in bone, and calcium reabsorption in the kidney. If left alone, high levels of blood cholesterol increase the risk of both Alzheimer's disease and heart disease. LDL, or so-called “bad cholesterol”, can also cause cells in both humans and mice to divide incorrectly and distribute their already-duplicated chromosomes unequally to the next generation, causing trisomy or monosomy.
“What is the cut off of how much sunlight we need in order to obtain enough vitamin D but also keep supplies of folic acid steady? Is it better to have less folic acid or less vitamin D?
There is no specific cut off for the amount of sunlight needed to keep the balance of vitamin D and folic acid. It is also not good to be lacking in folic acid or vitamin D, as both are integral to maintaining homeostasis. Folate is an important part of the cell growth system as well as helps produce red blood cells (52 Moalem). Vitamin D is important in the growth of bones, proper functioning of the heart, nervous system, clotting, and the immune system (50 Moalem).
Cholesterol, folic acid, and vitamin D relate to Big Idea 2 because they all work with your body to maintain homeostasis. They are also all components your body needs to function and grow, survive, and reproduce. Cholesterol is synthesized into vitamin D, which then uses energy to perform the various functions already mentioned. In the presence of UVB sunlight, the body makes vitamin D but destroys folic acid, which is also important to maintaining homeostasis.
Resources:
http://www.ncbi.nlm.nih.gov/books/NBK22339/
http://www.ncbi.nlm.nih.gov/pubmed/15585789
http://www.sciencedaily.com/releases/2013/04/130415182507.htm
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ReplyDeleteThe expression, “Too much of a good thing can be bad” is actually supported by scientific fact. Take our bodies for example, complicated systems in which many delicate balances have to be maintained for proper function. Balances such as our levels of cholesterol, vitamin D, and folic acid. These three concepts are discussed on pages 50-51. Cholesterol builds and maintains cell membranes and produces hormones.) It is crucial to the nervous system by helping the brain transmit messages, and also to the immune system by protecting against diseases such as cancer. Vitamin D is vital to the growth of healthy bones and the proper function of the heart, nervous system, the clotting process, and the immune system. Folic acid aids the body in DNA replication during cell division. All three of these components are necessary for survival, but there is a tricky relationship of interdependence between them. This is a representation of Big Idea 2 because it demonstrates how the body must maintain proper levels to achieve homeostasis that allows for our survival.
ReplyDeleteOn page 51, Moalem briefly discusses how cholesterol is responsible for the chemical process that produces vitamin D. He explains that UVB sunlight is required for our skin to convert cholesterol to vitamin D. The process of vitamin D synthesis is as follows: First, dehydrocholesterol (provitamin D3) is photolyzed by the light to become previtamin D3. Previtamin D3 spontaneously isomerizes to become vitamin D3, which continues on to undergo hydroxylation reactions in the liver and kidneys to become the active hormone, calcitriol.
Although cholesterol is essential for our survival, excess cholesterol has many negative impacts. Extra cholesterol is deposited in the arteries, which carries blood from the heart to the rest of the body. This can form a plaque buildup in the arteries which hardens and narrows the passageway, limiting the flow of oxygen-rich blood. One may experience dangerous medical conditions such as heart disease, blood clots, stroke, and even heart attack.
As important as exposure to sunlight is to create vitamin D, there is a trade off. UV light destroys folic acid reserves in our bodies. I agree with Tina’s point that there is no true “cut off” for the amount of sunlight people should receive. It varies greatly by person, as it depends on factors such as skin color and diet. Those with darker skin have greater protection against folic acid loss, but have a harder time absorbing vitamin D. The opposite goes for their lighter skin counterparts. Some people consume diets high in vitamin D and therefore don’t need to get as much sun, preventing folic acid destruction. I don’t believe having less folate or less vitamin D is better…both are essential to one’s health. If a person is short in folic acid or vitamin D, there are ways to attain it through supplements and diet.
Sources:
Survival of the Sickest by Dr. Sharon Moalem
http://www.ncbi.nlm.nih.gov/books/NBK22339/
http://www.nhlbi.nih.gov/health/health-topics/topics/hbc/
(Michelle Liang, mliang4@students.d125.org)