We spend a lot of time fretting about individual nutrients,
but often they work in tandem.
Nutrition guidelines and labels sometimes seem to have been
written one nutrient at a time. We're advised to get this amount
of that vitamin and that amount of this mineral. Separating out
nutrients this way makes the guidelines relatively easy to
understand and probably does help us avoid the classic diseases
of nutritional deficiency, such as scurvy (not enough vitamin C)
or pellagra (not enough niacin).
But good nutrition — and the way in which in our bodies absorb
and process nutrients — is a much bigger puzzle than a
nutrient-by-nutrient tally sheet suggests. Most nutrients don't
fly solo: they interact, join forces, cancel each other, jockey
for position on metabolic pathways. One reason food is so often
nutritionally preferable to pills or supplements is that food
contains a mixture of nutrients, so we benefit from their
interactions with each mouthful.
The following is a list of nutrients that work in pairs. It's
just a sampler, and far from a complete catalog. Even so, it may
help inform some food choices — and give just a taste of the
cruel complexity of the nutrition lurking behind guidelines and
Vitamin D and calcium
Like most nutrients, calcium is absorbed primarily in the small
intestine. If large quantities are present, much of the
bone-strengthening mineral diffuses across the inner lining of
the intestine on its own. But in smaller amounts, the mineral
gets absorbed with active assistance from vitamin D and several
of its metabolic offspring. D also lends a helping hand in the
absorption of phosphorus, another mineral important to keeping
bones strong and healthy, and magnesium. The evidence that D may
have wide-ranging benefits, including offering some protection
against heart disease and some forms of cancer, has piled up
lately. Some of these benefits may be the result of the vitamin's
absorption-related duties, but it may have a more direct effect
on disease processes and the immune system than previously
Right now, the official nutrition guidelines recommend that
adults get 1,000 milligrams (mg) of calcium and 400 international
units (IU) of vitamin D daily. For older adults, it's a bit more:
1,200 mg of calcium starting in your 50s and 600 IU of vitamin D
starting in your 70s. To give you an idea of how much that is, an
8-ounce glass of milk contains 300 mg of calcium and, because of
fortification, 100 IU of vitamin D.
There's debate these days about whether to revise the
recommendations to reduce the goal for calcium intake (or at
least de-emphasize it) and raise the goal for vitamin D (to 1,000
IU or even more).
Sodium and potassium
About 90% of the sodium we ingest comes in the form of sodium
chloride — salt, in common parlance. Sodium and chloride are
essential nutrients — we need them to maintain fluid levels in
the body — but the average American consumes thousands more
milligrams of sodium daily than he or she will ever need. Excess
sodium interferes with the natural ability of blood vessels to
relax and expand, while also encouraging the body to hang on to
water, so blood volume increases. "Uptight" blood vessels with
more blood flowing through them: that's a formula for
cardiovascular woe. Blood pressure goes up, and with it, the
chances of having a stroke or heart attack.
But potassium, because it encourages the kidneys to excrete
sodium, counters the harmful cardiovascular effects of sodium
surplus. Many studies have shown a connection between high
potassium intake and lower, healthier blood pressure. Several
have dug a little deeper and found that the potassium-to-sodium
ratio may be more important than potassium — or sodium — alone,
although precisely what the ratio should be is uncertain.
According to the current guidelines, American adults are supposed
to get 4,700 mg of potassium and 1,200 to 1,500 mg of sodium
daily, which works out to a ratio of somewhere between
four-to-one and three-to-one. The average American intake is
about half that amount of potassium (2,500 mg) and at least
double that amount of sodium (2,500–7,500 mg).
But time for a reality check: how many people are going to do the
math and keep track of their potassium-sodium ratio for the day?
It's enough for most of us just to count calories.
Fortunately, the take-home message is simpler. Almost all of us
need to have more potassium in our diets and a whole lot less
sodium. And the best way to do that is consistent with the
standard good nutrition playbook: load up on fruits and
vegetables (prime sources of potassium) and cut back on cookies,
salty snacks, fast foods, and ready-made lunches and dinners
(prime sources of sodium).
Vitamin B12 and folate
Vitamin B12 and folate form one of nutrition's more
estimable couples. They work together to support some of the most
fundamental processes of cell division and replication. They also
metabolize homocysteine together. And folate, which is itself one
of the eight B vitamins, depends on B12 to be
absorbed, stored, and metabolized. All this togetherness, despite
the fact that these two nutrients hail from different sides of
the animal-plant divide: vitamin B12 occurs naturally
in meat, eggs, milk, and other foods of animal origin, while the
best natural sources of folate include hard-core veggie fare like
leafy green vegetables, beans, and legumes. Fortification has
blurred these lines. Breakfast cereals with added vitamins and
minerals contain B12, and in the United States, by
law, cereal grains are fortified with folate. Indeed, because of
fortification, it's fairly easy to get the recommended amounts of
B12 (2.4 micrograms) and folate (400 micrograms) by
eating a reasonably well-balanced diet.
Strict vegans, who shun all animal-based products, may sometimes
struggle to get enough B12. But for the most part, it
isn't for lack of intake that B12 deficiency develops.
It typically occurs because of shortages of substances
inside the digestive system. Some people lack intrinsic
factor, a protein made by stomach cells that's needed for
B12 to be absorbed further down the pike, in the
ileum, the end portion of the small intestine. And many older
people secrete fewer of the gastric juices that break down
B12-containing compounds because they have atrophic
gastritis, an inflammatory condition that affects the lining of
Folate deficiencies occur for a number of reasons, including poor
diet, too much alcohol (alcohol interferes with the absorption of
folate), and B12 deficiency, because folate needs
B12 to be metabolized.
Deficiency in either or both vitamins may cause macrocytic
anemia, a form of anemia that results in enlarged red blood
Remedying a B12 deficiency can be pretty
straightforward. You can get injections every few months or take
a pill daily. Even if you're low on intrinsic factor or have
atrophic gastritis, the dose in the pills is often large enough
(1 mg) that an adequate amount of the vitamin gets absorbed.
Folate deficiencies can be corrected with multivitamins or folic
acid pills. In fact, folate from fortified food or a pill is
absorbed and metabolized almost twice as well as folate found
naturally in food. Similar to the B12–intrinsic factor
dynamic, if you ingest large amounts of folate, some manages to
get absorbed even if levels of its B12 partner are
There is an interesting twist to the B12-folate story.
Doctors often stumble upon the existence of a B12
deficiency by finding macrocytic anemia after ordering a routine
blood test. Tests for folate and B12 aren't usually
ordered. When someone with a B12 deficiency takes
folic acid supplements, those supplements can make the macrocytic
anemia go away — or prevent it from happening. But that
eliminates the most common clue to B12 deficiency, and
the deficiency itself may continue. B12 deficiencies
cause neurological problems, which range from mild tingling
sensations to memory loss, in addition to anemia. So people live
with neurological problems that might have been easily and
inexpensively treated with some extra B12.
Zinc and copper
We associate copper with pennies, wire, and pans, but it's also
an essential nutrient. Zinc is a little more familiar as an
edible substance, partly because people take zinc lozenges in the
belief that extra zinc shortens the duration of a cold (the
evidence is mixed on whether it actually does). Adults are
supposed to get 900 micrograms of copper daily. The daily zinc
goals are 11 mg for men and 8 mg for women. Neither mineral is
rare in the American food supply, so copper and zinc deficiencies
don't loom large in the nutritional worriment — with a couple of
Copper and zinc compete for absorption sites in the small
intestine. If there's a lot of zinc around, copper tends to lose
out and a copper deficiency may develop.
Some people in the early stages of macular degeneration, an eye
condition that can lead to blindness, are prescribed a special
vitamin-mineral combination, called AREDS, which has been shown
to slow down progression of the disease. The AREDS pills include
80 mg of zinc, enough to cause a copper deficiency, so 2 mg of
copper were added to the pills.
Another possible source of zinc overload is, of all things,
denture cream. A report published in 2008 in Neurology
described four cases of denture wearers with neurologic
abnormalities. Their problems were ascribed to a copper
deficiency from zinc exposure that came from using very large
amounts of denture creams. A neurologist at Harvard-affiliated
Beth Israel Deaconess Medical Center diagnosed a similar case of
denture cream–induced neurologic abnormality in 2009.
Niacin and tryptophan
Niacin is one of the B vitamins, although it rarely goes by its B
vitamin moniker, B3. These days, it's probably best
known for its cholesterol effects. Large doses (500 mg to 1,500
mg per day) lower "bad" LDL cholesterol and increase "good" HDL
cholesterol. Those pharmacological doses far exceed the amounts
needed for nutritional purposes. The daily niacin requirement is
16 mg for men and 14 mg for women.
Amino acids are the building blocks of protein, and tryptophan is
one of nine that we need to ingest because the body doesn't
synthesize them on its own. Tryptophan is important for several
reasons, but chief among them is its role as a supplier of
niacin, courtesy of some rather complicated metabolism. So one
way to avoid niacin shortfalls is to eat foods that contain a lot
of tryptophan. Chicken and turkey are high on that list.
Pellagra, now held up as the classic disease of niacin
deficiency, was once thought to be caused by a tryptophan
deficiency. The disease, which causes a bad rash, diarrhea, and
dementia, was common in the American South in the early 20th
century. How researchers traced it back to a niacin deficiency
and a corn-based diet is one of the great tales of nutritional
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