Today’s average restaurant meal is more than four times larger than in the 1950s, and according to the Centers for Disease Control and Prevention (CDC), adults are, on average, 26 pounds heavier. Despite the embarrassing abundance of food, many Americans still unknowingly suffer from nutrient deficiencies. Whether from vapid calories (hello, junk food), chemical-induced deficiencies, a lack of a variety, or any number of other factors, some of us just aren’t getting what we need.

The CDC’s Second Nutrition Report, an assessment of diet and nutrition in the U.S. population, concludes that there are a number of specific nutrients lacking in the American diet. Not only can nutrient deficiencies have long-lasting health effects, they can make you feel rotten. Here are some of the more common vitamins and minerals lacking in our diets, deficiencies that can cause an array of symptoms, from poor memory and bleeding gums to impaired work productivity and depression. 

1. Vitamin B12

Vitamin B12 is naturally found in many animal products, including fish, meat, poultry, eggs and dairy items; it is generally not found in plant foods. Fortunately for vegans, fortified breakfast cereals and some nutritional yeast products also contain vitamin B12. The vitamin is required for proper red blood cell formation, neurological function and DNA synthesis. Deficiency of this important vitamin is common, affecting up to 15 percent of the general population.

The Recommended Daily Allowance (RDA) for males and females over the age of 14 is 2.4 micrograms (mcg).

Symptoms of vitamin B12 deficiency include megaloblastic anemia, fatigue, weakness, constipation, loss of appetite and weight loss. Neurological problems like numbness and tingling in the hands and feet can also occur. Other symptoms include difficulty maintaining balance, depression, confusion, dementia, poor memory and soreness of the mouth or tongue. Vitamin B12 has also been linked to Alzheimer's disease.

2. Vitamin C

Most animals are able to synthesize vitamin C internally, but not humans; we need to get it from our food — lest we end up like the scurvy-ravaged sailors of lore. Citrus fruits, tomatoes, tomato juice and potatoes are major sources of vitamin C in the American diet. Other good contributors include red and green peppers, kiwi, broccoli, strawberries, Brussels sprouts and cantaloupe. Vitamin C is not naturally found in grains, but it is added to some fortified breakfast cereals.

The body uses vitamin C for the biosynthesis of collagen, L-carnitine and certain neurotransmitters, and it is also involved in protein metabolism. In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function and improves the absorption of nonheme iron. The RDA for adults over 19 is 90 milligrams (mg) for males and 75 mg for females.

Vitamin C deficiency causes scurvy, the symptoms of which include fatigue, malaise, inflammation of the gums, loosening or loss of teeth, joint pain, and poor wound healing. Although scurvy is no longer the scourge it once was, but narrowly chosen diets and bulimia among teens has created a scurvy resurgence. It can also afflict alcoholics or older people whose ability to absorb vitamin C has diminished from excessive medications or poor eating habits.

3. Vitamin D

Not many foods naturally contain Vitamin D. Fatty fish like salmon, tuna, mackerel, and fish liver oils are the best natural food sources. To a lesser extent, vitamin D is also found in beef liver, cheese, egg yolks and mushrooms. Fortified foods offer Americans most of the vitamin D they consume. Since the 1930s, nearly all of the U.S. milk supply has been fortified with 100 International units (IU) per serving. Breakfast cereals are also commonly fortified with vitamin D. And fortunately, our clever bodies make vitamin D when skin is exposed to sunlight; most people meet at least some of their vitamin D needs this way.

Vitamin D regulates calcium in the body and helps it to maintain strong bones. It is involved in healthy muscle movement, the nervous system relies on it, and it improves immune function as well as helping to reduce inflammation. The RDA for vitamin D is 600 IU for males and females between 19 and 70 years.

In children, vitamin D deficiency causes rickets, which has become less common since the 1930s but does still occur. With rickets, the bones become soft and bend. In adults, vitamin D deficiency leads to osteomalacia, causing bone pain and muscle weakness. Vitamin D deficiency has also been linked to daytime sleepiness.

4. Iodine

Iodine is a mineral found in ocean fish, seaweed, shrimp, and other seafood, as well as dairy products and products made from grains. Produce also contains iodine, although levels in fruits and vegetables depend on the soil they were grown in.

Iodine is used by the body to produce thyroid hormones that work to control other essential functions. Thyroid hormones are also required for proper bone and brain development during pregnancy and infancy. The RDA for those 14 years and older is 150 mcg.

Iodine deficiency during fetal and early-childhood development is a leading cause of brain impairments in much of the world. In adults, mild-to-moderate iodine deficiency can cause goiter, as well as impaired mental function and work productivity. Chronic iodine deficiency may be associated with an increased risk of some forms of thyroid cancer.

5. Iron

According to the World Health Organization, iron deficiency is the number one nutritional disorder in the world. Dietary iron comes in two forms, heme and nonheme. Heme iron is found in red meats, fish and poultry; nonheme iron is found in plants, like lentils and beans. Nonheme iron is the form that is added to enriched and fortified foods. Animal-derived iron is absorbed better than nonheme iron, but most dietary iron is nonheme iron. (Read more about iron for vegetarians here.)

Iron is essential for proper body functions. It helps transport oxygen to the cells, aids in blood cell creation, supports protein structures in the body and other important functions. The RDA for iron is 8 mg for males age 19-51, and 18 mg for females 19-51. For both males and females over 51, the RDA is 8 mg.

Symptoms of iron deficiency can include fatigue and weakness, poor work and school performance, slow cognitive and social development during childhood, difficulty maintaining body temperature, decreased immune function, increased susceptibility to infection, and inflamed tongue. (Read one writer’s experience with iron and overwhelming fatigue here.)

6. Magnesium

Magnesium is found in legumes, nuts, whole grains and vegetables, but American magnesium levels have dropped by half in the last century due to changes in agriculture and diet. Most Americans do not get the recommended amounts of magnesium, according to the experts.

Magnesium helps the body regulate more than 325 enzymes and plays an important role in organizing many bodily functions like muscle control, electrical impulses, energy production and the elimination of harmful toxins. The RDA for males 19-30 is 400 mg, and 420 mg for males 31 and over. Females 19-30 should aim for 310 mg; those 31 and over should get 320 mg.

Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures, personality changes, abnormal heart rhythms and coronary spasms can occur. One prominent study revealed that a magnesium-rich diet may lower stroke risk.

7. Zinc

Zinc is abundant in oysters, red meat, poultry and fortified breakfast cereals. Beans, nuts, whole grains and dairy products also provide some zinc, but beans and grains have compounds that keep zinc from being fully absorbed by the body. Because of this, vegetarians may need to eat twice as much zinc than what is recommended.

Zinc is important for helping the immune system battle bacteria and viruses. It also helps in the production of cells and during pregnancy and infancy; in childhood, zinc helps the body to develop correctly. Zinc helps wounds heal properly and plays a role in taste and smell. The RDA for zinc is 11 mg for adult men and 8 mg for adult women.

Symptoms of zinc deficiency include slow growth in infants and children, delayed sexual development in adolescents and impotence in men. Too little zinc can also be to blame for hair loss, diarrhea, eye and skin sores, loss of appetite, problems with wound healing, decreased ability to taste food, and lower alertness levels.

Note that some nutrients have upper limits as well, and overusing supplements can lead to adverse effects. (Also, some supplements can interfere with prescribed medications.) If you think you may be suffering from a nutrient deficiency, consult with your physician before loading up on supplements.

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