Lack of magnesium can make the body work harder to accomplish even low-intensity activities. It can also prompt abnormal heart rhythms. Some studies show that people with lower intakes or blood levels of magnesium are more likely to develop type 2 diabetes or heart disease than those who get plenty. Other studies don’t show a link between low magnesium and these chronic conditions.
Recommended intake: Current nutrition guidelines recommend that men get 420 milligrams a day of magnesium and women get 320 milligrams.
Good food sources: It’s fairly easy to meet your magnesium needs by food alone if you eat plenty of fruits and vegetables and whole grains. Cold breakfast cereals, which are often fortified with magnesium, are a good source. Cold cereals that are mostly whole grains are even better. Multivitamin-multimineral tablets usually contain about 100 milligrams of magnesium, which can help make up for shortfalls.
Safety: Healthy individuals have a hard time getting too much magnesium from food because the kidneys eliminate the excess in the urine. High doses of magnesium from supplements or medications can cause diarrhea, nausea, and abdominal cramping. Very large doses of magnesium, usually from laxatives and antacids, can cause dangerously low blood pressure, an irregular heartbeat, and cardiac arrest. There’s no tolerable upper limit of magnesium from food. From supplements it is 350 milligrams a day for adults.
POTASSIUM
Potassium is the most abundant positively charged particle inside your cells. Your body regulates the level of potassium in your bloodstream very carefully, because too much or too little can cause problems. A drop in potassium can make you feel weak and tired, trigger extra heartbeats (especially in people who already have heart disease), and cause muscle cramps or pain. Too little potassium combined with too much sodium may also cause high blood pressure, a condition shared by more than 50 million Americans.
Potassium Content of Some Foods
* * *
Food
Serving
Potassium (Milligrams)
% Daily Value*
Beet greens, cooked
1/2 cup
654
14
Tomato juice
1 cup
527
11
Baked beans
1 cup
509
11
Avocado
1/2 medium
487
0
Lima beans
1/2 cup
484
10
Cantaloupe
1 cup
473
10
Winter squash
1/2 cup
448
10
Pasta sauce, prepared
1/2 cup
422
9
Banana
1 medium
422
9
Spinach, cooked
1/2 cup
419
9
Orange juice
1 cup
378
8
Milk, 1%
1 cup
366
8
Figs, dried
large
333
7
Prunes
1/4 cup
318
7
Almonds
11/2 oz.
312
7
Raisins
1/4 cup
309
7
Black beans, cooked
1/2 cup
306
7
Potatoes, russet, baked with skin
1 medium
299
6
Yogurt
7 oz.
282
6
Peanuts, dry roasted
11/2oz.
270
6
Beets, cooked
1/2 cup
259
6
Turkey breast, baked
3 oz.
252
5
Pumpkin seeds, roasted
1/4 cup
232
5
Broccoli, cooked
1/2 cup
229
5
Collards, cooked
1/2 cup
214
5
Bran flakes
3/4 cup
160
3
Wheat germ
2 tbs
150
3
Tomatoes, raw
1/2 medium
146
3
Coffee
1 cup
116
2
* Based on a daily value for potassium of 4,700 milligrams in a 2,000-calorie-a-day diet.
Source: USDA National Nutrient Database for Standard Reference, Release 28, 2016, ndb.nal.usda.gov/ndb/foods.
Most Americans would be better off getting more potassium by eating at least five servings of fruits and vegetables each day, although they may not need to hit the daily target of 4,700 milligrams recommended by the National Academy of Medicine. That target is based on very limited evidence. Low potassium is a special problem for people who take diuretics to control high blood pressure and for those who drink a lot of coffee or other caffeinated beverages, because diuretics and caffeine increase the amount of potassium lost in urine.
Getting extra potassium in your diet, from food, from potassium salt, or from supplements, can lower high blood pressure or keep blood pressure in check. In so doing, it also reduces the chances of having the kind of stroke caused by the blockage of blood flow to the brain. Although the best way to ensure an adequate potassium intake is by eating lots of fruits and vegetables. Potassium salt substitutes can be helpful to people with hypertension, those who take diuretics, and heavy coffee drinkers. Don’t take potassium supplements unless you have discussed this with your physician, because they can be deadly when the kidneys aren’t working properly.
Recommended intake: The recommended dietary allowance for potassium is 4,700 milligrams a day for adults.
Good food sources: Bananas are famous for the amount of potassium they contain. But many other fruits and vegetables are also good sources. These include apricots, dates, kidney beans, oranges, spinach, nuts, seeds, and whole grains (see the table on page 228).
Safety: The Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine hasn’t set an upper limit for potassium. It is almost impossible to get too much from natural foods if your kidneys are working properly. If they aren’t, then you need to watch your potassium intake and have your blood level monitored. That’s because too much potassium in the bloodstream can cause deadly heart rhythms.
SODIUM
Sodium has gotten more attention than almost any other micronutrient. Sodium is an essential part of our diet, but most Americans get more than they need. It’s hard not to. Prepared foods are often loaded with table salt, which is one-third sodium. A cup of boxed macaroni and cheese or an order of Burger King salted french fries can deliver more than 1,000 milligrams of sodium—most of a day’s healthy ration. It’s also often found where you least expect it: a cup of pasta sauce can have almost half of a day’s healthy salt allotment (see “Hidden Salt in Food” on page 230).
Although the “daily value” for sodium listed on food labels is 2,300 milligrams, the average person actually needs less than 1,000 milligrams a day to keep his or her systems in good working order. That’s less than half a teaspoon of salt. Yet the average American gets more than three times that amount, about 3,500 milligrams of sodium. The excess is excreted, but not always before it can do some damage. Excess sodium pulls water from cells and thus increases blood pressure, especially in people whose genes make them more sensitive to salt.
Hidden Salt in Food
* * *
Foo
d
Serving
Sodium (Milligrams)
% Maximum Recommended Daily Limit*
Kielbasa, pan-fried
1 link
3,870
168
Arroz con grandules (restaurant)
1 order
3,807
166
Orange chicken (restaurant)
1 order
3,583
156
Applebee’s crunchy onion rings
1 serving
2,916
127
Vegetable chow mein (restaurant)
1 order
2,673
116
Kung pao chicken with rice
2 cups
2,610
113
Ham sandwich with mayo and tomato
6 inches
2,130
93
Burger King Whopper with cheese
1
1,431
62
Chicken pot pie
1 small
1,187
52
Canned sauerkraut
1 cup
939
41
Baked beans, canned
1 cup
871
38
Dill pickles
1 (3 oz.)
833
36
Chicken noodle soup, canned
1 cup
831
36
Corned beef brisket
3 oz.
827
36
Tuna salad submarine sandwich
6 inches
780
34
Cheese pizza, pepperoni
1 slice
773
34
Macaroni and cheese, canned
1 cup
737
32
Lasagna, frozen
1 serving
639
28
Pasta sauce, prepared
1/2 cup
577
25
KFC biscuit
1
540
23
American cheese
1 slice
468
20
Green beans, canned
1 cup
461
20
Cottage cheese
1/2 cup
459
20
Vegetable juice cocktail
1 cup
428
19
Light tuna, canned
3 oz.
337
15
McDonald’s french fries
large
290
13
Waffle, frozen
1
223
10
Raisin bran cereal
1 cup
210
9
Frozen peas
1/2 cup
58
3
* Based on a daily value for sodium of 2,300 milligrams in a 2,000-calorie-a-day diet.
Source: USDA National Nutrient Database for Standard Reference, Release 28, 2016, ndb.nal.usda.gov/ndb/foods.
Scientists agree that consuming too much sodium promotes high blood pressure. Whether reducing sodium reduces the risk of cardiovascular disease has been controversial, but the overall evidence strongly supports a benefit of limiting sodium intake, even though the optimal target is not clear. Cutting back on sodium is often one of the first things that health care providers suggest to people who have just been diagnosed with high blood pressure, along with stopping smoking and getting more exercise. For years, the results of salt reduction studies were inconsistent and controversial. But the Dietary Approaches to Stop Hypertension (DASH) II study, which carefully controlled the amount of salt in participants’ diets, showed that aggressively cutting back on salt had an important effect on blood pressure.36 This has been supported by other carefully controlled studies. As described in chapter eight, the first DASH trial also clearly showed that eating more fruits and vegetables can substantially lower blood pressure.
Documenting the “best” sodium intake has been difficult. One reason is that it’s hard to measure how much sodium individuals consume because this mineral is hidden in so many processed foods. In addition, long-term trials of sodium intake are difficult to do because keeping people on low-sodium diets is difficult in an era when high-sodium and hidden-sodium foods are everywhere.
The most effective way to keep blood pressure low combines weight loss (if needed), eating plenty of fruits and vegetables rich in potassium, and staying away from foods high in salt.
The bottom line is that a salty diet doesn’t do you any good and can be harmful, so cutting out unnecessary salt makes sense.
Recommended intake: The National Academy of Medicine and the 2015–2020 Dietary Guidelines for Americans recommend getting no more than 2,300 milligrams of sodium a day. The American Heart Association, meanwhile, recommends getting no more than 1,500 milligrams a day. The rationale for a lower target is that further decreasing sodium intake to that level helps further reduce blood pressure, which is a strong risk factor for cardiovascular disease.
Good food sources: Sodium isn’t the kind of nutrient you need to look for—it finds you. Rather than searching for foods that are good sources of sodium, most people need to seek low-sodium foods. Almost any unprocessed food—vegetables, fruits, grains, nuts, meats, dairy foods and the like—are low in sodium.
Safety: The Food and Nutrition Board set 2,300 milligrams of sodium a day as its upper limit. More than that isn’t immediately harmful but can nudge you toward developing high blood pressure, which over a lifetime affects 90% of Americans.
SELENIUM
The mineral selenium is a potent antioxidant, but it probably doesn’t contribute to good health in that way. Instead, it helps several enzymes break down peroxides, powerful oxidizing agents made throughout the body that can damage DNA and tissues.
To date, there’s no convincing evidence to show that, in the United States, too little selenium increases the risk of cancer or other chronic conditions or that taking a selenium supplement prevents them. In the 1980s, selenium was added to fertilizer in Finland, where the soil level—and thus intake—were low. Although blood levels of selenium rose dramatically, cancer rates didn’t budge. The Nutritional Prevention of Cancer study showed that taking extra selenium, 200 micrograms a day, may have offered some protection against skin cancer.37 However, the Selenium and Vitamin E Cancer Prevention Trial (SELECT), established to look at prostate cancer, did not support the finding on skin cancer. It failed to answer the question about selenium and prostate cancer because only one case of fatal prostate cancer occurred during the trial.38
In some regions of China and other parts of the world with very low soil levels of selenium, low intakes of this mineral has led to a unique form of heart disease.
Recommended intake: The recommended dietary allowance for selenium is 55 micrograms a day for adults.
Good food sources: Many foods contain selenium. Brazil nuts, seafood, beef, eggs, and spinach are good sources, but their selenium content depends on the soil levels or feed used to produce the food.
Safety: Selenium is toxic at high doses, with a tolerable upper intake of 400 micrograms a day for adults. As with other micronutrients, it’s hard to take in that much selenium from food. Getting too much from supplements can cause brittle hair and nails, upset stomach, skin rash, bad breath, and extreme exhaustion. Some types of Brazil nuts deliver a lot of selenium because of the high levels in the soil where they are produced. If you frequently consume them, try to eat a variety of nuts instead so you don’t get too much selenium.
ZINC
You may have seen the “cold-fighting zinc lozenges” near the checkout counter of your local pharmacy or grocery store. These lozenges have been the topic of many trials to determi
ne whether they truly shorten the duration of colds. More than a dozen studies have been conducted among people just developing colds, some of whom took zinc and some of whom didn’t. The results have been inconsistent. However, in two recent meta-analyses, cold sufferers who popped the unpleasant-tasting zinc lozenges reduced their symptoms by about one to two days on average compared with those taking placebo lozenges.39
There’s no question that zinc plays a key role in keeping the immune system healthy. It also acts as an antioxidant, is needed for proper vision, and is involved in blood clotting, wound healing, and the normal development of sperm cells. Does this mean you should reach for a zinc supplement? No. Despite the fact that most Americans actually get less than the recommended daily amount of zinc, there’s little evidence that such low intakes cause health problems. Studies looking at colon cancer, prostate cancer, prostate inflammation (prostatitis), and macular degeneration have not shown a clear link with zinc intake.
Some people need extra zinc. Children need enough of this mineral for growth and development. Too little zinc may be one of the ways that undernourishment slows brain development and motor skills, contributes to hyperactivity, and causes problems with attention. Older people may need extra zinc for several reasons. They tend to consume less zinc than younger people. They often have trouble absorbing zinc from food. The medications they take, especially diuretics for high blood pressure, can increase zinc excretion. And the extra fiber and calcium they may take can bind zinc and make it unavailable to the digestive system. Heavy drinkers, people with digestive problems such as Crohn’s disease and ulcerative colitis, and those with chronic infections also need extra zinc.
Recommended intake: The recommended dietary allowance for zinc is 8 milligrams a day for women and 11 milligrams a day for men. Women who are pregnant or breastfeeding need a bit more (12 milligrams a day instead of 8) for themselves and the children they are carrying or feeding.
Eat, Drink, and Be Healthy Page 30