Vitamin C

What Is Vitamin C?

Vitamin C is the common name for ascorbic acid. People, along with other primates, guinea pigs, and birds, are unable to make vitamin C. Other animals and plants can make their own vitamin C from glucose. Vitamin C has long enjoyed popularity as a nutrition supplement and continues to be one of the most recognizable and sought after nutrients.

What Are Food and Supplement Sources of Vitamin C?

When we think of good sources of vitamin C, citrus fruits instantly come to mind. However, other fruits and some vegetables such as strawberries, tomatoes, and broccoli can make a significant contribution to our vitamin C intake (Table 9.2). Ascorbic acid (L-ascorbic acid) is a popular nutrition supplement and there isn't an advantage to supplementing vitamin C extracted from plants or synthetic (laboratory made) forms. Supplement makers often manufacture ascorbic acid-mineral combinations (for example, sodium ascorbate and calcium ascorbate) that are less acidic than ascorbic acid. These forms can help people who find ascorbic acid irritating to their stomach.

Table 9.2 Vitamin C Content of Select Fresh Foods

Food

Vitamin

Food

Vitamin

C (mg)

C (mg)

Fruits

Vegetables

Orange juice (1 cup)

124

Green peppers (% cup)

95

Kiwi (1)

108

Cauliflower, raw (% cup)

75

Grapefruit juice (1 cup)

94

Broccoli (% cup)

70

Cranberry juice cocktail

90

Brussels sprouts (% cup)

65

(1 cup)

Collard greens (% cup)

48

Orange (1)

85

Cauliflower, cooked (% cup)

30

Strawberries (1 cup)

84

Potato (1)

29

Cantaloupe (%)

63

Tomato (1)

23

Grapefruit (1)

51

Raspberries (1 cup)

31

Watermelon (1 cup)

15

Does Vitamin C Break Down After Fruit/Vegetable Harvest and During Cooking?

Vitamin C is susceptible to breakdown during certain cooking, processing, and storage procedures (that is, heat or cooking in neutral or basic mediums). For instance, potatoes can lose nearly half of their vitamin C by boiling. Spinach can lose nearly all its vitamin C if stored for 2 to 3 days at room temperature. Thus, for practical purposes, citrus fruits and other vitamin C-containing fruits and vegetables usually are better dietary sources of vitamin C as they are generally eaten uncooked and shortly after harvest.

How Much Vitamin C Is Absorbed?

Vitamin C is fairly well absorbed from our digestive tract when consumed in typical dietary amounts. However, as the amount of vitamin C increases in our diet its absorption efficiency decreases. For example, a vitamin C intake of 180 milligrams (two times the RDA for an adult man) is about 80 to 90 percent absorbed, while for an intake approximating 5 grams, only about one quarter is absorbed. However, 25 percent absorption of 5 gram is still about 1.2 gram of vitamin C. Much of this excessive vitamin C will be quickly removed from the body in the urine.

How Much Vitamin C Do We Need?

The Recommended Dietary Allowance (RDA) for vitamin C for adult men and women is 90 and 75 milligrams, respectively. During pregnancy and lactation the RDA increases to 85 and 120 milligrams for adult women. This is the level of vitamin C that will provide for good blood and organ vitamin C status for most adults. Meanwhile an intake of 400 milligrams for healthy adults is recommended by many nutritionists to ensure that the levels in the blood and cells are optimal.

Where Is Vitamin C Found in Our Body?

Vitamin C is found in most of the tissue throughout the body with greater concentrations in the heart, brain, pancreas, adrenal glands, thymus, and lungs. Two of the most vitamin C-dense regions in the body are the pituitary gland and the lens of the eye. Vitamin C status in the body is typically assessed by measuring serum levels as well as the level of white blood cells. The former is more reflective of recent dietary intake while the latter is a better indicator of tissue stores. As vitamin C circulates in the blood it is vulnerable to kidney filtration and subsequent loss in the urine either as ascorbic acid or derivatives (metabolites) such as oxalates.

Vitamins Are Vital Molecules in Food 195 What Roles Does Vitamin C Play in Our Body?

The activity of vitamin C is realized in its ability to either donate or accept electrons. In doing so it participates in many metabolic processes. Perhaps its most famous role is its involvement in the production of collagen. However, vitamin C plays a role in the production of other vitamin molecules including carnitine, norepinephrine, and bile acids.

Vitamin C is a potent antioxidant and supports the production of bile, collagen, carnitine, and norepinephrine.

Collagen is a connective tissue protein and is found in teeth, bone, tendons, ligaments, cartilage, and arteries. Vitamin C is fundamentally involved in modifying specific amino acids in the collagen protein which ultimately affects collagen's structure and function. Without vitamin C, the collagen that is made is relatively worthless.

Norepinephrine functions as a neurotransmitter in the brain and in organs to regulate their function as well as a hormone released from the adrenal glands during exercise and fasting. Among other operations nor-epinephrine is involved in the "fight or flight" response which helps us deal with stressful and threatening situations. Norepinephrine is made from the amino acid tyrosine and vitamin C plays a role in the conversion process.

Carnitine is needed to use longer chain length fatty acids for energy, as it basically chaperones these fatty acids into the mitochondria of our cells where they can be broken down for ATP production. The making of carnitine in the liver requires vitamin C among other substances.

Bile acids are produced in the liver and are vital for efficient fat digestion and absorption. Since bile acids are derived from cholesterol, which in turn decreases the amount of cholesterol that circulates, vitamin C plays a role in lowering the risk of heart disease.

Vitamin C is also an antihistamine factor and an immune function potentiator, and is involved in the making of thyroid hormone, serotonin, and steroid hormones.

Vitamin C enhances iron absorption from our digestive tract. This means that both iron and vitamin C would need to be part of the same meal for this to occur.

Is Vitamin C a Potent Antioxidant?

One role of vitamin C, which is receiving more and more attention today, is that of antioxidant. Antioxidants serve as lines of protection against free radicals, as discussed in Chapter 1. Antioxidants provide protection against free-radical activity that can lead to heart disease, cancers, and other medical concerns, so this role of vitamin C is more of a nutraceutical role. Not only does vitamin C serve as potent antioxidant it can also reactivate other antioxidants, namely vitamin E.

What Happens If We Don't Get Enough Vitamin C?

Poor consumption of fruits and vegetable sources of vitamin C, as well as smoking can reduce vitamin C status in the body. This in turn can lower antioxidant protection and over time could reduce the efficiency of other vitamin C roles in the body. Meanwhile, true vitamin C deficiency syndrome is referred to as scurvy. For adults, scurvy will appear approximately 1 to 3 months after discontinuing vitamin C consumption. Medical signs and symptoms include impaired wound healing, fluid buildup in ankles and wrists (edema), swollen, bleeding gums with tooth loss, fatigue, lethargy, and joint pain. In infants who are not breast-fed, deficiency can be recognized at around 6 months of age when the vitamin C stores transferred from the mother during pregnancy have been exhausted. Medical signs of this syndrome (Moeller-Barlow disease) include abnormal bone character and development, severe joint pain, anemia, and fever. The abnormalities in bone are directly related to vitamin C's involvement in the proper manufacturing of collagen.

What Happens If Too Much Vitamin C Is Consumed?

If you set out to increase your vitamin C intake through the use of supplements, a couple of possible side effects and a practical issue should be considered. First, as discussed, as vitamin C intake increases, the efficiency of absorption decreases. This still leads to more vitamin C absorbed per day, but a proportionate increase in urinary loss of vitamin C and its metabolites also occurs. Perhaps one of the biggest concerns associated with consuming gram-size doses ("gram dosing") is gastrointestinal discomfort since it is an acid. Furthermore, large concentrated doses can promote diarrhea. Otherwise supplementation of a couple grams of vitamin C daily is pretty safe. The latest DRI Upper Limit is set at 2 grams for adults.

Can Vitamin C Prevent or Treat Colds?

As an antioxidant and also an immune function potentiator, vitamin C has been suggested for use in decreasing the incidence and severity of the common cold. Research to date suggests that vitamin C supplementation probably won't decrease the incidence of colds; however it might lessen the severity, especially for some athletic populations. However, starting vitamin C supplementation at the onset of symptoms does little to decrease the severity.

Thiamin (Vitamin B1)

What Is Thiamin?

Thiamin is classically known as vitamin B1 and sometimes aneurine. It was identified in the 1930s and was one of the first substances to be classified as a vitamin. Along with the other water-soluble vitamins (except vitamin C and choline), thiamin is a B-complex vitamin. The most salient role of B-complex vitamins is their involvement in energy metabolism.

What Foods Have Thiamin and Which Form Is Found in Supplements?

Thiamin is found widely distributed in foods, although most contain low concentrations. Brewer's yeast, pork, and whole grain and enriched grain products are good sources of thiamin (Table 9.3). Thiamin is found is nutritional supplements and for fortification as thiamin hydrochloride and thiamin nitrate (for example, thiamin mononitrate).

How Much Thiamin Do We Need?

The RDA for men and women is 1.2 and 1 milligrams of thiamin respectively. Meanwhile the RDA for pregnant and lactating women is 1.4 milligrams. Because thiamin is important in energy operations it might be more appropriate to express thiamin recommendations based on level of additional calories burned during exercise and sport training/ competition. Here recommendations of 0.5 milligrams of thiamin would be recommended for every 1,000 calories expended daily. Thus athletes

Table 9.3 Thiamin Content of Select Foods

Food

Thiamin (mg)

Food

Thiamin (mg)

Meats

Grains

Pork roast (3 ounces)

0.8

Bran flakes (1 cup)

0.6

Beef (3 ounces)

0.4

Macaroni (V cup)

0.1

Ham (3 ounces)

0.4

Rice (V cup)

0.1

Liver (3 ounces)

0.2

Bread (1 slice)

0.1

Nuts and seeds

Vegetables

Sunflower seeds (% cup)

0.7

Peas (V cup)

0.3

Peanuts (% cup)

0.1

Lima beans (V cup)

0.2

Almonds (% cup)

Corn (V cup)

0.1

Fruits

Broccoli (V cup)

0.1

Orange juice (1 cup)

0.2

Potato (1)

0.1

Orange (1)

0.1

Avocado (V)

0.1

expending 3,000 to 6,000 calories daily would have a recommendation of 1.5 and 3 milligrams. See Table 3.2 for recommended levels for children and teens.

Does Thiamin Break Down During Cooking?

Similar to vitamin C, thiamin is not very stable during cooking processes. Convection cooking of meat may result in destruction of roughly half of its thiamin content. The baking of breads and the pasteurization of milk may result in destruction of approximately 25 percent and 15 percent of thiamin content, respectively. In light of its water-soluble nature, some thiamin may also be washed away in the thaw drip. The thaw drip is the watery fluid that drains from thawing meats. In addition, certain fish and shellfish contain natural thiaminases, which are enzymes that break down thiamin. Fortunately, cooking inactivates these enzymes.

Where Is Thiamin Found in Our Body?

Most of the thiamin that we eat is absorbed in the small intestine. Once in the body, thiamin does not seem to have a primary organ of storage, however, the brain, kidneys, liver, and skeletal muscle seem to have higher concentrations. In fact, because of its high energy demands, the brain accounts for as much as one-half of the total thiamin in the body. Thiamin circulates around primarily aboard red blood cells (RBCs) and the activity of a thiamin-associated enzyme is used to gauge thiamin status. Thiamin and its metabolites are subject to removal from the body in urine.

What Does Thiamin Do in Our Body?

Thiamin serves as a coenzyme in many key reactions in the cells. A coenzyme is a substance that will interact directly with an enzyme; together the two allow a chemical reaction to proceed. The enzyme will not function optimally without the presence of the coenzyme. Many water-soluble vitamins function as coenzymes. Thiamin is active in the form of thiamin pyrophosphate (TPP) which is a coenzyme for a couple of enzymes involved in energy pathways. As a co-enzyme, thiamin is involved in complete carbohydrate, protein, and fat breakdown for energy (Figure 9.1).

Thiamin is involved in energy metabolism, DNA, and ATP formation as well as proper functioning of muscle and the brain.

Glycolysis Glucose--—--y Pyruvate

Glycolysis Glucose--—--y Pyruvate

Figure 9.1 Chemical reaction pathways in our mitochondria allow for electrons (black dots) to be removed from involved molecules and they are carried to electron transport chains found in the mitochondria membrane (inner). The carriers are niacin and riboflavin based.

Thiamin is also involved in converting glucose to ribose in the cells. Ribose, and a slightly modified form, deoxyribose, are key components of deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). You will remember that DNA provides the instructions or blueprints for making cells, while RNA is involved in translating the blueprints into the construction of proteins.

What Does Thiamin Do in the Brain and Muscle?

Without question thiamin is crucial to the proper functioning of the brain, nerves, and muscle. However, the exact involvement of thiamin may not be easily explained within the confines of thiamin's classic energy-support functions. Thiamin appears to have the ability to increase the efficiency of the electrical events that allow nerves and muscle to function properly. Interestingly, when thiamin is deficient in the diet the brain tends to hold on to its thiamin more vigorously than other tissues do. This suggests that a very special relationship exists between the brain and thiamin. We will discuss thiamin's role in the aging brain and conditions such as Alzheimer's disease in Chapter 12.

What Happens If Too Little Thiamin Is Consumed?

If thiamin is deficient from our diet for several weeks, symptoms will begin to appear. Classic thiamin deficiency has been termed beriberi, which is often separated into two types. Wet and dry beriberi describe the effects of thiamin deficiency with special reference to the presence of fluid buildup in tissue (edema). Enlargement of the heart sometimes occurs and appears to be more prevalent in those individuals with the fluid buildup (wet beriberi). Muscular weakness, loss of appetite, and atrophy of legs are also characteristic symptoms of thiamin deficiency. Beriberi is said to mean "I can't, I can't," which probably refers to the deficits in voluntary movement that accompany thiamin deficiency.

An infant who is breast-fed by a thiamin-deficient mother is also at risk of thiamin deficiency. This situation, called infantile beriberi, typically occurs between 2 and 6 months of age, and these infants may lose their desire to eat, may regurgitate milk, and may also experience vomiting and diarrhea. A rapid heart rate and a bluish tint to the skin may also develop.

Can Alcohol Consumption Affect Thiamin Status?

Mild alcohol consumption doesn't impact thiamin status in the body. However, the heavy, chronic alcohol consumption of an alcoholic increases the risk for thiamin deficiency for a couple of reasons. Diet in alcoholism is typically low in thiamin along with other essential nutrients. Furthermore, there appears to be a reduced ability to absorb thiamin in the digestive tract of alcoholic people, with an accompanying increase in metabolic need for this vitamin.

Can Too Much Thiamin Be Consumed?

Because much of excessive thiamin will be rapidly removed from the body in the urine, excessive consumption of thiamin appears relatively safe. In fact, the current DRIs do not include a Tolerable Upper Limit for thiamin. However, long-term thiamin intake of greater than 100 times the RDA (1,200 milligrams) has been associated with headaches, convulsions, weakness, allergic reactions, and irregular heart rhythms.

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