GLOSSARY OF NUTRIENTS
My disclaimer: I am not a doctor or a nutritionist. I am merely
interested in the subject. This material is from books and other sources I
have, and while I have tried very hard to be accurate, it is important to
remember that this was written by a layman, and I assume no responsibility
for any errors it contains or the results anyone obtains from adhering to
This area is not nearly finished. I would like this page to become a state
of the art summary of current nutrition. Readers are encouraged to add
information or make comments.
VITAMIN B-2 - Riboflavin
Riboflavin is a water soluble coenzyme which is a constituent of two
important enzymes, FMN and FAD, involved in the production of bodily
energy from food. It is necessary for cell respiration and also for the
production and regulation of certain important hormones, including insulin.
Exercise increases the need for riboflavin. Riboflavin is also necessary
for the formation of red blood cells, the maintenance of good vision, skin,
nails, and hair. It is involved with an enzyme called glutathione
reductase, which helps maintain glutathione, one of the most important
anti-oxidants. Riboflavin itself also has anti-oxidant qualities. One
visible symptom of riboflavin deficiency is cracks in the corners of the
mouth or on the lips. Riboflavin deficiency can result in the formation
The amount of B-2 in most foods is so small that it is difficult to obtain a
sufficient supply without supplementation. Good sources are liver, tongue,
and other organ meats, milk, yogurt, eggs, almonds, whole grains, mushrooms,
soybeans, oysters, and green leafy vegetables. Milk, which contains
riboflavin, should not be stored in clear bottles, since sunlight can
destroy this vitamin within a few hours. However, riboflavin is not
destroyed by cooking.
Dosage and Toxicity
The recommeded daily allowance is 1.7 mg for men, 1.3 mg for women, and
.8 mg for infants. There is no known toxicity of riboflavin.
VITAMIN B-3 - Niacin
Niacin functions in the body as a component in the coenzymes NAD and NADP,
which are involved in over 50 different chemical reactions in the body.
Niacin-containing enzymes play an important role in the breakdown of foods,
particularly carbohydrates, and the production of energy. Niacin is vital
to the nervous system and for formation and maintenance of skin, tongue,
and digestive system tissues. It is necessary for the regulation of blood
sugar, the formation of sex and adrenal hormones, formation of red blood
cells, and is a detoxifying agent - a substance that can cleanse the body of
many toxins and other pollutants. It is very effective in improving
circulation and reducing the cholesterol and fat level in the blood.
Specifically, niacin lowers LDL (bad) cholesterol, Lp(a) lipoprotein,
triglyceride and fibrinogen levels, while simultaneously raising HDL (good)
cholesterol levels. It is water soluble. Niacin is available in
nutritional supplements as either niacin (nicotinic acid or nicotinate) or
niacinamide (nicotinamide). The nicotinic acid form is very effective in
reducing blood cholesterol levels whereas the niacinamide form is useful in
arthritis and early-onset type 1 diabetes.
The niacin "equivalent" listed in dietary tables means either pure niacin or
the amino acid tryptophan, which the body can convert into niacin. Good
sources are liver, lean meats, eggs, poultry, fish, peanuts, and green peas.
Wheat germ is also a fairly good source. Niacin is quite resistant to heat
Dosage and Toxicity
The recommeded daily allowance is 19 mg for men, 15 mg for women, and 5-6 mg
for infants. The RDAs for niacin are based on calorie intake: 6.6 mg of
niacin per 1,000 calories. People with peptic ulcers, liver disease, gouty
arthritis, asthma, or significant heart rhythm disturbances should take
niacin only with the advice of a physician. No real toxic effects are
known; but large doses, usually 100 or more mg, may cause passing side
effects such as tingling and itching sensations, intense flushing of the
skin, and throbbing in the head due to a dilation of the blood vessels. The
flushing effect is caused by a sudden release of histamine, hence the
cautions for people with asthma or peptic ulcers. By taking it as
niacinamide, these side effects are eliminated. Taking more than 2 grams of
niacinamide might cause liver damage. Exercise, trauma, or illness may
increase requirements. Since niacin is involved in the release of stomach
acid, patients taking large doses should take the vitamin on a full stomach.
Deficiency leads to an illness called pellagra.
VITAMIN B-5 - Pantothenic Acid
Pantothenic acid is a water soluble coenzyme which occurs in all living
cells and is synthesized in the human body by intestinal bacteria. Indeed,
its name comes from the Greek word pantos meaning "everywhere." It is
essential for fat, carbohydrate, and protein metabolism and energy
production. It works together with carnitine and coenzyme Q-10 in
fatty-acid transport and utilization. Pantothenic acid plays a role in the
manufacture of red blood cells and the neurotransmitter acetylcholine, as
well as the manufacture of cortisone and other adrenal hormones important
for healthy skin and nerves. It has long been called the "antistress"
vitamin because of its central role in adrenal function and cellular
metabolism. It is essential for the synthesis of fats, cholesterol, and
bile, and aids in the utilization of other vitamins, particularly
riboflavin. It is important in maintaining a healthy digestive tract.
Recently a metabolite of pantothenic acid called pantothene has been the
subject of research because of its ability to lower cholesterol levels.
Pantothenic acid may be useful in treating rheumatoid arthritis.
Good sources are organ meats, egg yolks, milk, fish, poultry, avocado,
peanuts, mushrooms, and whole grain cereals. About 33% of the pantothenic
acid content of meat is lost duringcooking and about 50% of the content of
flour is lost during milling. Pantothenic acid is widely distributed in
foods so a deficiency is rare.
Dosage and Toxicity
There is no official RDA for pantothenic acid, but there is a Safe and
Adequate intakes recommendation. This is 2mg - 3 mg for infants and 4-7 mg
for adults. There are no known toxic effects of pantothenic acid.
VITAMIN B-6 - Pyridoxine
Vitamin B-6 is a water soluble coenzyme required for the proper functioning
of more than 60 enzymes. Its primary role involves protein and its building
blocks, the amino acids. B-6 aids in the conversion of one amino acid to
another, the synthesis of new amino acids from carbohydrates, the conversion
of amino acids to carbohydrate or fat for storage or energy, and the
conversion of the amino acid tryptophan to niacin. It is also essential for
the synthesis of RNA, DNA, red blood cells, all amino acid neurotransmitters
(e.g. serotonin, dopamine, melatonin, epinephrine, norepinephrine, etc.),
and prostaglandins (hormone-like substances that regulate a variety of body
processes including blood pressure, muscle contraction, and heart function).
Vitamin B-6 is also critical in maintaining hormonal balance and proper
immune function. It is involved in the breakdown of food for body energy and
in the release of glycogen from the liver and muscles. For this reason, it
is essential to physical activity. It also plays a role in cell
multiplication. Therefore, tissues which replicate rapidly are strongly
influenced by B-6 availability, e.g. red blood cells, immune system cells,
skin, mucous membranes, and also in pregnancy. A B-6 deficiency results in
depressed immunity, noted by a reduction in the quantity and quality of
antibodies, shrinkage of lymphatic tissues (including the thymus gland),
decreased thymic hormone activity, and a reduction in the number and
activity of lymphocytes. B-6 is also required for the proper absorption of
vitamin B-12, and for the production of hydrochloric acid and magnesium.
It also helps linoleic acid function better in the body. Vitamin B-6 helps
maintain the balance of sodium and potassium, which regulates body fluids
and promotes the normal functioning of the nervous and musculoskeletal
systems. It is useful in treating asthma and carpal tunnel syndrome (a
painful disorder caused by compression of nerves in the wrist). In general,
asthmatics have a defect in the metabolism of the amino acid tryptophan
and reduced platelet transport of serotonin, possibly as a result of low
B-6 levels. Studies show that some asthma patients benefit from B-6
Vitamin B-6 is a family of coumpounds that includes pyridoxine, pyridoxal,
and pyridoxamine. The best sources are meats and whole grains, particularly
liver, poultry, fish, wheat germ, soybeans, hazlenuts, walnuts, lentils, and
Dosage and Toxicity
B6 requirements are based on protein metabolism, so the more protein
consumed, the more B-6 is needed. The recommended dietary allowance is
geared for a diet containing 100 grams of protein per day. The RDA is
2 mg for men, 1.6 mg for women, and .3 mg - 1 mg for infants, depending on
age. Excessive amounts of B-6 can cause neurological problems. Too much
B-6 without zinc can lead to numbness and tingling in the fingers and toes.
No more than 50 mg a day should be taken without consulting a physician.
VITAMIN B-12 - Cobalamin
Vitamin B-12 is a bright red crystalline compound because of its high
content of cobalt. Vitamin B-12, like folic acid, functions as a "methyl
donor" to other molecules, including cell membrane components and
neurotransmitters. A methyl donor is a compound that carries and donates
methyl groups (CH3). As a methyl donor, B-12 plays a critical role in
proper energy metabolism, immune function, nerve function, and is involved
in homocysteine metabolism. Homocysteine, a metabolite of the amino acid
methionine, damages the cells that line arteries, leading ultimately to
atherosclerosis and heart disease. It is also a factor in the progression
of osteoporosis. Vitamin B-12 works with folic acid in many body processes,
including the synthesis of DNA, RNA, red blood cells, the insulation (myelin
sheath) that surrounds nerve cells, and enabling the conduction of signals
along nerve cells. B-12 helps both iron and carotene (provitamin A)
function better in the body and aids folic acid in the synthesis of choline.
In order to absorb the small amounts of B-12 found in food, the stomach
secretes intrinsic factor, a mucoprotein enzyme that binds to B-12 and
assists its absorption in the lower small intestine. Autoimmune reactions
in the body can bind the intrinsic factor or even prevent cells from
producing it, preventing B-12 absorption.
Vitamin B-12 is found in sugnificant quantities only in animal foods, so
vegetarians are frequently deficient. The best sources are liver, clams,
kidney, and oysters, many types of fish, eggs, cheeses, liver, kidney, lamb,
pork, beef, veal, and yogurt. Some of the vitamin is lost when cooked to
temperatures above about 100 degrees centigrade (the boiling point of
Dosage and Toxicity
The recommended dietary allowance is 2 mcg a day for adults and .3-.7 mcg a
day for infants, depending on age. Unlike other water soluble nutrients,
which cannot be stored well, B-12 is stored in the liver, kidney, and other
body tissues. As a result, deficiency symptoms may not show themselves
until intake has been poor for five or six years. Deficiency of B-12 leads
to pernicious anemia, a deadly type of anemia characterized by large,
immature red blood cells. No one has ever reported clear toxicity from
vitamin B-12. Vegeterians must take a B-12 supplement, unless they
regularly eat egg products. Vegetarian or macrobiotic diets are frequently
low in B-12 but high in folic acid which may mask the deficiency. Vitamin
B-12 cannot be made synthetically and must be grown, like penicillin, in
bacteria or molds.
VITAMIN C - Ascorbic Acid
A primary function of vitamin C is the formation and maintenance of collagen,
a protein that forms the basis for the most abundant tissue in the body:
connective tissue. Collagen acts as a cementing substance between cells.
Collagen is the supporting material in blood vessel walls, and is found, for
example, in bones, teeth, skin, tendons, and the cornea of the eye. It also
maintains the shape of discs of the backbone. Vitamin C is vital for wound
repair, healthy gums, the prevention of easy bruising, and the prevention of
hemorrhaging. Cells in arterial walls need collagen to help them expand and
contract with the beats of the heart; it is also needed in the capillaries
which are more fragile. Vitamin C is critical to the manufacture of certain
nerve transmitting substances and hormones, to carnitine synthesis, and aids
in forming red blood cells. Vitamin C has a significant relationship with
other nutrients and is part of the metabolism of some amino acids that end
up as hormones, such as thyroxin, phenalynine, and tyrosine. Vitamin C
converts the inactive form of folic acid to the active form, folinic acid,
and plays a role in calcium and iron metabolism. Vitamin C is a very
important antioxidant. It protects thiamine, riboflavin, folic acid,
pantothenic acid, and vitamins A and E against oxidation and protects the
brain and spinal cord from destruction by free radicals. Vitamin C also
works with antioxidant enzymes such as glutathione peroxidase, catalase,
and superoxide dismutase. The exact role of vitamin C in enhancing the
immune system is hotly debated, but many people believe that taken in
quantities of several grams a day, it can diminish the likelihood and
severity of many diseases, particularly the common cold. This point of
view was brought to world attention in 1970 by Nobel Prize winning chemist
Linus Pauling in his book, "Vitamin C and the Common Cold." Often, studies
which dispute this viewpoint use quantities of vitamin C which even
proponents believe are too small to produce an effect. Vitamin C affects
various immune functions by enhancing white blood cell function and activity
and increasing interferon levels, antibody responses, antibody levels,
secretion of thymic hormones, and integrity of ground substance.
Vitamin C also possesses many biochemical effects similar to interferon.
Increasing one's intake of bioflavonoids increases absorption of vitamin C.
Vitamin C is water soluble. Deficiency of vitamin C results in a condition
known as scurvy, the symptoms of which are bleeding gums, loosened teeth,
poor wound healing, extensive bruising, susceptibility to infection, tender
joints, aching bones, and muscle cramps. In fact, "ascorbic," is Latin for
The best sources are citrus fruits, and vegetables, especially peppers,
turnips, broccoli, potatoes, brussels sprouts, cauliflower, cabbage, and
spinach. Vitamin C is destroyed by exposure to light, heat, or air.
Dosage and Toxicity
Humans, apes and guinea pigs are among the very few animals that are unable
manufacture vitamin C in their bodies, and, thus, must rely on dietary
sources. The recommended dietary allowance is 60 mg for adults and 30-40 mg
for infants, depending on age. Vitamin C is extremely safe in most people.
Extremely large doses may produce minor side effects in some people. The
primary concern with high dosages often cited in medical literature is the
development of calcium oxalate kidney stones. However, numerous studies
demonstrate that in persons not on hemodialysis or suffering from recurrent
kidney stones, severe kidney disease, or gout, high dosages do not cause
Vitamin D is a fat soluble nutrient which can be acquired either by
ingestion or by exposure to sunlight. It is the only vitamin for which
the biologically active form is also a hormone. The sun's ultraviolet rays
activate a form of cholesterol in the skin, converting it to vitamin D.
Before it becomes active, it is altered by the liver; then the kidneys
change it again into its active form which is called dihydroxy. There are
two major food forms of vitamin D - vitamin D2 (ergocalciferol) and vitamin
D3 (cholecalciferol). Vitamin D2 is the form most often added to food,
particularly milk, and the form most often found in nutritional supplements.
Vitamin D helps maintain bone growth and health by promoting bone
mineralization. It helps synthesize enzymes in the mucous membranes which
are involved in the transport of calcium. It is necessary for normal
growth in children, for without it, bones and teeth do not calcify properly.
It plays a role in maintaining a stable nervous system, normal heart action,
and normal blood clotting, because all these functions are related to the
body's supply and utilization of of calcium and phosphorous. Vitamin D
maintains calcium and phosphorous in the blood by stimulating their
absorption in the GI tract, mobilizing calcium and phosphorous out of the
bones into the blood, and stimulating retention by the kidney. Beyond bone
metabolism, vitamin D receptors are located in the kidney and intestine. In
fact a large number of tissues are responsive to vitamin D, including the
islet cells of the pancreas that produce insulin, the bone marrow cells
responsible for the production of specialized immune cells called monocytes,
the parathyroid gland, the ovaries, certain brain cells, developing heart
muscle, and breast cells. Since 1985, there has been evidence to suggest
that vitamin D helps protect against cancer, particularly breast and colon
cancer. Apparently vitamin D plays a role in the control of cellular
proliferation and differentiation. An epidemiologic map of the US showing
mortality rates from breast and colon cancer reveals that the rates are
highest in populations exposed to the least amount of sunlight. There is
speculation that chronic vitamin D deficiency finally shows up as cancer of
the breast and colon. Vitamin D is best utilized when taken with vitamin A.
Ingested vitamin D is absorbed with the fats through the intestinal walls
with the aid of bile. As with other fat soluble vitamins, vitamin D
requires at least a small amount of fat in the diet for absorption. Vitamin
D formed in the skin by the action of sunlight is absorbed into the
circulatory system. The production of vitamin D on the surface of the skin
is blocked by skin pigment. The darker the skin, the less readily vitamin D
is formed. Sunscreen factors of 8 or above prohibit synthesis of vitamin D
in the skin. In the summer, adequate stores of vitamin D are probably
obtained from ten minutes of sunbathing. After absorption from the
intestine or formation in the skin, vitamin D is transported to the liver
for storage; other deposits are found in the skin, brain, spleen, and bones.
In children, a deficiency of vitamin D results in a bone disorder called
rickets. In adults, a deficiency results in osteomalacia, an adult form of
rickets. Vitamin D deficiency is often seen in elderly people who do not
get any sunlight, particularly those in nursing homes.
Fish liver oils are the best natural source of both vitamins D and A. Other
good sources are cold-water fish (mackerel, salmon, herring, sardines,
etc.), liver, shrimp, butter, and egg yolks.
Dosage and Toxicity
WARNING: Vitamin D can be toxic if taken in doses of more than four times
the RDA. Quantities are expressed in International Units. 100 IU is
equivalent to 2.5 micrograms of cholecalciferol. The recommended dietary
allowance is 400 IU for adults up to about 24, 200 IU for older adults, and
300 IU for infants. These figures are for someone who has very little
exposure to ultraviolet light. Prolonged exposure to sunlight does not
cause vitamin D toxicity. The body has an efficient feedback system and
reduces the production of vitamin D with increased exposure to sunlight.
VITAMIN E - Tocopherol
In 1922 researchers discovered that when rats were fed a diet missing
vitamin E, they became unable to reproduce. The name tocopherol comes
from the Greek words "tokos," which means "offspring," and "phero," which
means "to bear." Seven forms of tocopherol exist in nature: alpha, beta,
delta, epsilon, eta, gamma, and zeta. Of these, alpha tocopherol has the
most biological value. Vitamin E is necessary for all oxygen-consuming
life forms. Vitamin E is an antioxidant, which means it opposes oxidation
of substances in the body. Oxidation involves a compound called an
oxidizer which attacks another compound, removing an electron from it.
Vitamin E protects other substances by being oxidized itself, taking the
brunt of any attack on lipids or other components of the cell membranes.
Vitamin E prevents saturated fatty acids and vitamin A from breaking down
and combining with other substances to form substances that may be harmful
to the body. Fat oxidation results in the formation of free radicals.
Free radicals are highly reactive, and therefore destructive, molecules
that can cause extensive damage to the body. In particular, they can damage
nerve cells and damage (alter) DNA. Vitamin B complex and vitamin C are
also protected from oxidation when vitamin E is present in the digestive
tract. Fats and oils containing vitamin E are less susceptible to rancidity
than those without vitamin E. It has the ability to unite with oxygen and
prevent it from forming toxic peroxides. This leaves the red blood cells
more fully supplied with the pure oxygen that the blood carries to the heart
and other organs. Vitamin E prevents red blood cells from destruction by
free radicals such as hydrogen peroxide and also prevents oxidation of the
pituitary and adrenal hormones. Since aging in the cells is now believed to
be partially due to free radical damage, vitamin E and other antioxidants
are believed by some to retard aging. Vitamin E is actually incorporated
into the fatty portion of cell membranes where it acts to stabilize and
protect these structures, not only from free radicals, but also from
compounds such as lead, mercury, and other heavy metals; toxic compounds
such as benzene, carbon tetrachloride, and cleaning solvents; drugs; and
radiation. The first sign of vitamin E deficiency is the rupture of red
blood cells, which have become fragile, probably as a result of free radical
oxidation of the polyunstaurated fats in the membranes. Vitamin E is
important to immune function. Since it is known that vitamin E protects red
blood cells, the improvement in immunity may be due to a similar protection
of white blood cells.
Vitamin E is not only an antioxidant, it is also of great importance in
energy production. It plays an essential role in cellular respiration af
all muscles, especially cardiac and skeletal. The vitamin makes it possible
for these muscles and their nerves to function with less oxygen, thereby
decreasing their endurance and stamina. Vitamin E also causes dilation of
the blood vessels, permitting a fuller flow of blood to the heart. It aids
in bringing nourishment to the cells and strengthening the capillary walls.
It is a highly effective antithrombin in the bloodstream, inhibiting
coagulation of blood and preventing clots from forming. It works to treat
and prevent heart diseases such as coronary thrombosis, a heart attack in
which the vessels are blocked by blood clots. Vitamin E causes arterial
blood clots to disintegrate. It is also succesful in treating angina
pectoris, a chest pain resulting from an insufficient flow of blood to the
heart. It aids rheumatic heart disease and early stages of cardiac
complications by returning abnormal capillaries to normal and reducing
fluid accumulation within and between cells. Vitamins E and C and
bioflavonoids, along with exercise, have been used to help treat varicose
veins. Vitamin E allows greater storage of and reduces the requirement for
vitamin A. Many studies have shown that low vitamin E levels increase the
risk of certain types of cancer, particularly cancers of the GI tract and
Vitamin E, like the other fat soluble vitamins is absorbed in the presence
of bile salts and fat. It is stored mostly in the liver.
Tocopherols occur in greatest concentrations in cold-pressed vegetable oils,
all whole raw seeds and nuts, whole grains, soybeans, eggs, spinach, peaches,
prunes, and avocados. Wheat germ oil is the source from which vitamin E was
Dosage and Toxicity
The recommended dietary allowance of vitamin E is 15 IU (International Units)
for males, 12 IU for females, and 4.5 to 6 IU for children. The amount of
vitamin E required is dependent on the amount of polyunsaturated fats in the
diet. The more polyunsaturated fats consumed, the greater the risk they
will be damaged. Since vitamin E prvents this damage, as the intake of
polyunsaturated fattys acids increases, so does the need for vitamin E.
Vitamin E may produce side effects in high doses. It is probably not a good
idea to take much more than 800 IU a day. There are several substances that
interfere with vitamin E in the body. For example, when vitamin E and the
inorganic form of iron are administered together, the absorption of both
substances is impaired. Therefore, in nutritional supplements, vitamin E
and iron should be taken at least 8 hours apart. Selenium has been found
to increase the benefits of vitamin E and therefore it is suggested that
they be taken together. Note that large quantities of selenium are toxic.
In supplements, the natural form, d-alpha-tocopherol is biologically more
active than the synthetic form, dl-apha tocopherol.
Calcium is the most abundant mineral in the body. About 99% is in the bones
and teeth. The remaining 1% is involved in the soft tissues, intracellular
fluids, and blood. The ratio of calcium to phosphorous in the bones is 2.5
to 1. It is absorbed in the small intestine with the help of vitamin D.
The major function of calcium is to act in cooperation with phosphorous to
build and maintain bones and teeth. The calcium content of the bones is
constantly fluctuating based the amount the body can get from the diet in
comparison to its needs. Calcium is found in two different forms in the
bones. One form is bound tightly and is not easily removed. A second
form can be easily removed from bone to aid in maintaining normal blood
calcium levels. The 1% of ionized calcium that circulates in the fluids of
the body is small but vital to life. It is essential for the production and
activity of numerous enzymes, the contraction of muscles, release of
neurotransmitters, regulation of heartbeat, the clotting of blood, helps
prevent the blood from becoming to acidic or too alkaline, helps regulate
the passage of nutrients through cell walls, helps maintain the body's
connective tissue, particpates in the structuring of DNA and RNA, and
activates the digestive enzyme lipase. Calcium also eases insomnia and
protects against colon cancer. Studies have shown that people with colon
cancer consume less calcium and vitamin D than cancer-free persons. When
the blood's calcium concentration is too high, hormones and vitamin D cause
the calcium to be deposited in the bones. Bone metabolism depends on an
interplay of many nutritional and hormonal factors. Calcium and vitamin D
are the most important factors. In women, estrogen aids in the
incorporation of calcium into the bone.
Calcium deficiency in children may lead to a bone disorder called rickets.
In adults it may lead to osteomalacia, an adult form of rickets. Low
calcium intake will also lead to osteoprosis (porous bones), which currently
affects more than 20 million people in the United States.
The primary source of calcium is dairy products. Plant foods rich in
calcium include tofu, kale, figs, sunflower seeds, wheat bran, olives,
broccoli, and oranges. Oysters and almonds are good sources too.
Dosage and Toxicity
The recommended dietary allowance is 800 mg for adults and 400 mg - 600 mg
for infants, depending on age. Teenagers and young adults require 1,200 mg.
Calcium supplements are generally well tolerated at dosages less than
2,000 mg. Higher dosages increase the risk for kidney stones and soft
tissue calcification. In choosing a calcium supplement, one should
consider the following facts. Bone meal contains absorbable calcium, but
may be contaminated with lead. Calcium chloride may be irritating to the
stomach. Calcium phosphate interferes with the absorption of other
nutrients when it is included with them in a supplement. Both calcium
carbonate and magnesium carbonate (not the easiest to absorb) are found in
dolomite. Calcium gluconate, calcium lactate, and calcium citrate are the
best absorbed, but they are lower in strength.