RDI - Vitamin C August 6, 2008 1:40 am
Posted by tungtide in Answers.Tags: nutrition, RDA, RDI, vitamin C, vitamins
5 comments
Following up on my post about recommended daily intakes of various vitamins, Janelle requested more information about a specific vitamin. In this case I’m focusing on Vitamin C, also known as ascorbate.
The structure of Vitamin C is seen to the left. It’s similar in structure to some simple sugars. Of course, none of that is really all that useful, it’s the function of Vitamin C that’s of issue here.
The compound is capable of functioning as an antioxidant and a cofactor in the synthesis of endogenous compounds. See Wiki. Again, I’m not a fan of going to Wikipedia as my major source but the information seems to be useful.
Among the important functions is the stabilization of the formation of collagen. Vitamin C deficiency causes the condition known as scurvy, which is an inability of collagen to function properly. Collagen is one of the major supporting macromolecular structures in the body, produced by cells known as fibroblasts. Loss of collagen in scurvy is seen as:
Scurvy leads to the formation of spots on the skin, spongy gums, and bleeding from all mucous membranes. The spots are most abundant on the thighs and legs, and a person with the ailment looks pale, feels depressed, and is partially immobilized. In advanced scurvy there are open, suppurating wounds and loss of teeth.
Humans are not capable of synthesizing the compound, unlike most other living organisms, which is why an exogenous source is necessary.
The recommended daily intake is centered, at least initially, on dosages that are sufficient to prevent scurvy. The US RDA recommends 75 mg (female) and 90 mg (male) of Vitamin C per day with an upper limit of 2000 mg per day. I knew nothing about the controversy surrounding high-dose Vitamin C until just recently. Some scientists are claiming that the RDA is nothing more than a minimal dose to prevent disease, while a larger dose is capable of providing increased antioxidant protection and a host of other good things.
The problem that I see is twofold: One, doses above the 2000 mg/day upper limit are known to cause diahrrea and intestinal problems (some detractors claim this is how you know it’s working) indicating a deviation of the body away from normal homeostasis. Two, For the most part the body will use what it’s given to the extent that it’s needed. Large doses of Vitamin C are likely to be excreted without being used in any way.
It would seem then, that the RDA for Vitamin C is an effective dose to maintain health and avoid one of the more annoying downsides of life as a pirate. It is possible to take doses at 1000% of the RDA and still be within accepted tolerances for daily dosing without side effects.
As always, feel free to chime in with follow-up questions or corrections.
Recommended Daily Intake July 28, 2008 1:15 pm
Posted by tungtide in Answers.Tags: minerals, nutrition, RDA, RDI, RDV, vitamins
8 comments
About a week ago Janelle posted this question:
How do they come up with the recommended daily allowance for the various vitamins and minerals?
I initially tried doing some research and didn’t find much in the way of an interesting answer. Unfortunately in the intervening time I haven’t been able to expand my research on the subject. As a result this is going to be a short answer that mainly comes from Wikipedia.
The RDA was developed during World War II by Lydia J. Roberts, Hazel K. Stiebeling and Helen S. Mitchell, all part of a committee established by the U.S. National Academy of Sciences in order to investigate issues of nutrition that might “affect national defense.”
The allowances were meant to provide superior nutrition for civilians and military personnel, so they included a “margin of safety.” Because of food rationing during the war, the food guides created by government agencies to direct citizens’ nutritional intake also took food availability into account.
The Food and Nutrition Board subsequently revised the RDAs every five to ten years. In the early 1950s, USDA nutritionists made a new set of guidelines that also included the number of servings of each food group in order to make it easier for people to receive their RDAs of each nutrient.
For the current recommendations the following guidelines are used:
- Estimated Average Requirements (EAR), expected to satisfy the needs of 50% of the people in that age group.
- Recommended Dietary Allowances (RDA), the daily dietary intake level of a nutrient considered sufficient to meet the requirements of nearly all (97–98%) healthy individuals in each life-stage and gender group.
- Adequate Intake (AI), where no RDA has been established, but the amount established is somewhat less firmly believed to be adequate for everyone in the demographic group.
- Tolerable upper intake levels (UL), to caution against excessive intake of nutrients (like vitamin D) that can be harmful in large amounts.
- The RDA is used to determine the Recommended Daily Value (RDV) which is printed on food labels in the U.S. and Canada.
This does not really answer the question about how the regulations were developed, but covers the history of the way we came about the guidelines.
I can follow up with information about specific nutrients if desired, but this is well out of my area of expertise and requires some research. I dislike having Wikipedia as my sole reference, but it’s a place to start.
Growth Hormones June 25, 2008 9:08 pm
Posted by Bret in Uncategorized.Tags: beef, cow, growth hormone, milk
5 comments
In response to Janelle’s question: “Have there been any significant changes to farm animals’ biology and behavior in the last few decades due to the increased use of growth hormones? Could our interference actually change or speed up their evolution as a species?”
Hormonal therapy has become an integral part of large animal veterinary medicine and livestock production. We use reproductive hormones to manipulate the estrus cycle of females to increase breeding efficiency, give hormones to animals to alter growth and development (largely for economic benefit) and remove naturally occurring hormones from animal to alter behavior and reproductive potential (spaying and neutering animals). So first some background information on growth hormones used in the animal industry:
Growth hormones have one basic principle, to increase production of an economically desirable commodity. Usually this is in the form of meat or milk. We’ll talk about these separately. First, to increase carcass yield from meat animals you must begin with an animal that has the potential to grow to your desired specifications, basically the genetic capability to grow, gain weight and convert feed to muscle mass. Hormonal additives are typically in the form of ear implants composed of estrogens, progesterones, synthetic anabolic steroids or a combination thereof. Estrogen and progesterone stimulate a natural release of growth hormone (GH) in higher levels than would naturally occur. This engages a cascade of metabolic processes that lower overall catabolism and increase the retention of amino acids by the animal’s body, thus leading to a significant gain in muscle mass over the animals life. Anabolic steroids are typically only used just prior to slaughter (if at all) for a short period of time as they create rapid growth but can sacrifice the quality of the meat if overused. So, growth hormone itself is not given, but rather other naturally occurring hormones are used to stimulate to animals body to produce its own GH.
When it comes to using hormonal therapy in increasing milk production the concept is similar. Recombinant bovine somatotropic hormone (rbST) has been widely publicized recently, especially in California where the dairy industry is huge. It is given to cows when they achieve peak lactation, typically about 10-12 weeks post-calving. It is a naturally occurring growth hormone that re-directs the use of absorbed nutrients to increase the milk yield over the course of an entire lactation. The cow does not produce more milk that she would naturally produce in a day at her peak lactation, but rather maintains that peak lactation for a longer period of time, thus increasing yield over the course of a lactation period (about 10 months). The cow isn’t over-milked or worn out as is often perceived, and no studies to this point have shown an increase in mastitis (udder infection) or other health issues.
These hormone supplements are perfectly safe for use and have all been approved by the FDA. When it comes to meat animal “enhancement” the animals receiving the treatment are not going to be used for breeding (and are usually steers or spayed heifers) and thus the effects are terminal and not propagated in the species. If these hormones are given to breeding animals they will usually have deleterious effects on reproductive capability and thus prevent any changes from entering the future gene pool. This is similar to men using anabolic steroids and having reduced testicular capacity due to negative feedback on hormonal regulation. rbST in dairy cows also does not alter the genetics of the cow or her offspring but may make it more difficult for that particular cow to be re-bred with the efficiency desired on large dairies (studies vary on conception rates in cows using rbST). They still breed back, it can just take longer under normal management practices.
Our interference with these additives is not altering the evolution of these species, but our breeding selections and genetic manipulations are certainly placing pressure on all species to change. This is nothing new and has been ongoing since humans first domesticated animals and sought out desired characteristics. I am not aware of any effects these additives have on behavior but I will look into it. I’m sure Dave will have something to say about the biotechnology and genetic modification of animals lately…
Accelerated Cows June 20, 2008 2:51 am
Posted by tungtide in Answers.Tags: biology, evolution, selective pressures
4 comments
Janelle’s second question was aimed at Bret (our resident animal expert) and me.
Have there been any significant changes to farm animals’ biology and behavior in the last few decades due to the increased use of growth hormones? Could our interference actually change or speed up their evolution as a species?
I am ill-equipped to answer the first part of that question. The second part I think I can take a stab at.
Our interference in the development of any domesticated species (cats, dogs, cows, pigs, etc.) is affecting the evolution of those species. Dogs are an excellent example of what selective breeding and isolate populations can produce. While all dogs are still technically the same species, it is physically impossible for some breeds to reproduce (think St. Bernard and Chihuahua).
The increased use of growth hormones (and I assume you were thinking of cows in this example) can have an effect on the development of the species. Again, I’ll have to defer to Bret to talk about significant changes in the animals themselves. From a moelcular biology perspective (which is where I usually sit) the addition of an exogenous hormone will change gene expression and protein production in the cows. The intended consequence is increased milk production or better quality beef. Because of the complexity of the systems and the uncertainty of long-term effects on the animals, there may be additional changes that we are unaware of.
Biological systems like to find an equilibrium. When something is added (external hormone, genetic activation) or knocked out (gene knockout animals are common in research) there are compensatory changes in the animal. Other pathways, genes, and proteins will be activated/deactivated in unexpected ways to attempt to create a “normal” functioning animal.
Cows injected with hormones will almost certainly develop a resistance to the chemcial (regardless of whether it is a normally-occuring hormone or not) and will find a balance of self-regulation that will try to keep the cow in “cow form” as much as possible.
If this is extended over may generations and in an isolated population, it may begin to select for genes and pathways that are not normally expressed in cows. So, yes, there is the potential for accelerating the evolution of animals through these treatments.
Why do we rarely see tornadoes strike major cities? June 20, 2008 12:11 am
Posted by imemerson in Uncategorized.1 comment so far
It is a common myth that cities are safe from tornadoes, spawned from the fact that we mostly see tornado damage in small towns and suburbs here in the U.S. The answer to this question can be found by looking at any map of the U.S. or looking out the window while flying. The area of the U.S. covered by cities is very small compared to the area covered by farmland, suburbs, and small towns. Hence, the odds of a tornado striking a major city are very small compared to one hitting a small town.
The Center for Severe Weather Research at the National Center for Atmospheric Research reached the same conclusion. In the U.S., the area known as Tornado alley stretches from Colorado and Wyoming in the west to Ohio in the east, North Dakota in the north to Texas and Louisiana in the South (see map here). There are roughly two dozen major metropolises in this area, but they make up only a small fraction (less than 1%) of the total area. Thus, it is more likely a tornado will strike an area that does not contain a major city.
Dr. Fujita at the University of Chicago (for whom the tornado intensity scale is named) suggested that urban heat island effects may have an impact on small tornadoes. His thinking was that the increased heat levels in the center of major metropolises may disrupt the formation of small tornadoes (which make up the majority of tornado strikes). This assertion has not been proven or disproven and weather researchers continue to investigate the impact of cities on tornado formation.
Developments June 18, 2008 4:11 pm
Posted by tungtide in Answers.Tags: genomics, molecular biology, proteomics, science
4 comments
Janelle has posed a couple of questions, so I’ll deal with her initial one first:
What would you say is the most promising research going on in your field today, both with respect to technological advancements (which will eventually affect the general public) and with respect to broadening our general knowledge of science (which the general public probably doesn’t care about)?
This was a little difficult to answer at first because my field of expertise (if you can call me that) is in pharmacology and toxicology. I deal with the way drugs and toxicants interact with biological systems. From this field I reach into metabolism, physiology, neurology, and most other biologic sciences. It leaves me in a position where I know a little about a lot of fields and a lot about a few smaller fields.
To me the most exciting prospects are in the “-omics” areas: genomics, transcriptomics, and proteomics. Genomics is a term that most people know, dealing with the study of the genome. Projects to decode the human genome have been completed and many other animals and microbes are underway. This is not news though. The biggest difficulty in genomics is the vast amount of data. It only gets more complicated. Even when we reach the point where we can look at the entire genome of an individual it does not tell us the whole story: just because the “code” is built into the DNA does not mean that we know anything about the use of it. The central dogma of molecular biology is:
DNA –> RNA –> Protein
While there are exceptions to this rule, the central dogma leads us from genomics to transcriptomics looking at the expression of mRNA from the coding regions of DNA. Understanding the expression of mRNA adds a level of context to the DNA code. No longer is it simply potential, but the DNA has actually “produced” a product that is measurable. The production levels of mRNA are highly variable and depend upon the presence of outside drugs, the diet and health of the individual, the environment surrounding that individual, and the base code in the DNA. What transcriptomics can tell us is the rate and extent of activation of a specific region of coding DNA. There is still a further complication.
Proteomics is the study of the proteins expressed in a cell, tissue, or organism. While the presence of mRNA can tell us the extent to which a region of DNA was transcribed it does not provide correlative data with protein expression. Said another way: DNA tells you what the cell is capable of, RNA tells you what’s being activated, but protein tells you what the call can actually do. Proteins are the major players in the cell. They catalyze reactions, provide structure, and can act as signaling molecules.
What does all this mean? I don’t want to go into more details about protein structure and function but I want to pull back from the details and try to hit the big picture. Drug development focuses on finding compounds that can affect biological systems. The drugs themselves are often either small molecules or protein derivatives. The better we understand the genomics, transcriptomics, and proteomics of humans the better the drugs can be.
Here’s a hypothetical situation or two:
Person A needs a drug for high blood pressure. Company X makes a small molecule antagonist (SMA) for receptor Q. The SMA will interact with Receptor Q and prevent it’s function, affecting production of the renin-angiotensin system and lowering blood pressure.
Situation 1: Person A has a mutant form of Receptor Q with an altered active site that responds appropriately to the endogenous (normal) compounds in the body but has only a 10% binding of the SMA compared to the wildtype receptor. In this case a genomic analysis would provide information about the mutation and alert the doctor. The solution would be to use a different SMA that was designed specifically for the mutant receptor. Why would we not simply increase the dose of the original SMA? You run the risk of providing a toxic dose, increase the chances of drug-drug interactions if the patient is on other medications, and it gets expensive.
Situation 2: Person A has a normal form of Receptor Q but is unresponsive to the SMA drug or any mutant-designed forms. Genomic analysis shows that the DNA sequence is normal, and mRNA analysis shows that production is at expected levels. However, there’s no protein reaching the cell surface (where many receptors are located). Proteomic analysis of the cell would reveal that a shuttling protein in the endoplasmic reticulum (for this example assume the shuttling protein is specific for this receptor, otherwise the person would be dead) is mutated and instead of sending Receptor Q to the cell surface, it sends it to the proteasome for degradation. The solution here is less clear, but would likely mean trying a different approach to controlling hypertension through another mechanism.
The reason I brought all this up is because science is discovering more levels of complexity in the interactions of cellular machinery. A better understanding of all levels of this machinery will lead to better and safer medicine and improve the overall human condition.
Questions? June 17, 2008 5:57 am
Posted by tungtide in Uncategorized.7 comments
If nobody’s going to ask any questions I’m going to start talking to myself.
Anyone interested in drug interactions and herbal supplements? I can talk about that for hours.
Congratulations, it’s a….blog? June 14, 2008 10:45 pm
Posted by tungtide in Uncategorized.add a comment
I had no idea that the Scientition blog was going to be born today, only that its arrival was on the horizon. I haven’t much else to say that isn’t already covered better in the Hello World introduction.
Please, email us, use the comments section and ask your questions. Otherwise, I’ll have to start asking myself questions and that will be followed by name calling, face punching, and a drunken stupor…actually that might be fun too.
Hello world! June 14, 2008 10:01 pm
Posted by imemerson in Uncategorized.add a comment
That title’s pretty funny if you ever took a computer programming class.
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