Many nutrients are absolutely essential for good health.
It is possible to get most of them from a balanced, real food-based diet.
However, the typical modern diet lacks several very important nutrients.
This article lists 7 nutrient deficiencies that are incredibly common.
Iron is an essential mineral.
It is a main component of red blood cells, where it binds with hemoglobin and transports oxygen to cells.
There are actually two types of dietary iron:
- Heme iron: This type of iron is very well absorbed. It is only found in animal foods, and red meat contains particularly high amounts.
- Non-heme iron: This type of iron is more common, and is found in both animal and plant foods. It is not absorbed as easily as heme iron.
Iron deficiency is one of the most common nutrient deficiencies in the world, affecting more than 25% of people worldwide (, ).
This number rises to 47% in preschool children. Unless they're given iron-rich, or iron-fortified foods, they are very likely to lack iron.
30% of menstruating women may be deficient as well, due to monthly blood loss. Up to 42% of young, pregnant women may also suffer from iron deficiency.
Additionally, vegetarians and vegans have an increased risk of deficiency. They consume only non-heme iron, which is not absorbed as well as heme iron (, ).
The most common consequence of iron deficiency is anemia. The quantity of red blood cells is decreased, and the blood becomes less able to carry oxygen throughout the body.
Symptoms usually include tiredness, weakness, weakened immune system and impaired brain function (, 6).
The best dietary sources of heme iron include:
- Red meat: 3 ounces (85 g) of ground beef provides almost 30% of the RDI ().
- Organ meat: One slice of liver (81 g) provides more than 50% of the RDI.
- Shellfish, such as clams, mussels and oysters: 3 ounces (85 g) of cooked oysters provide roughly 50% of the RDI.
- Canned sardines: One 3.75 ounce can (106 g) provides 34% of the RDI.
The best dietary sources of non-heme iron include:
- Beans: Half a cup of cooked kidney beans (3 ounces or 85 g) provides 33% of the RDI.
- Seeds, such as pumpkin, sesame and squash seeds: One ounce (28 g) of roasted pumpkin and squash seeds provide 11% of the RDI.
- Broccoli, kale and spinach: One ounce (28 g) of fresh kale provides 5.5% of the RDI.
However, you should never supplement with iron unless you truly need it. Too much iron can be very harmful.
Bottom Line: Iron deficiency is very common, especially among young women, children and vegetarians. It may cause anemia, tiredness, weakness, weakened immune system and impaired brain function.
Iodine is an essential mineral for normal thyroid function and the production of thyroid hormones ().
Thyroid hormones are involved in many processes in the body, such as growth, brain development and bone maintenance. They also regulate the metabolic rate.
Iodine deficiency is one of the most common nutrient deficiencies in the world. It affects nearly one-third of the world's population (, , ).
The most common symptom of iodine deficiency is an enlarged thyroid gland, also known as goiter. It may also cause an increase in heart rate, shortness of breath and weight gain ().
Severe iodine deficiency may also cause serious adverse effects, especially in children. These include mental retardation and developmental abnormalities (, ).
There are several good dietary sources of iodine:
- Seaweed: Only 1 g of kelp contains 460–1000% of the RDI.
- Fish: 3 ounces (85 g) of baked cod provide 66% of the RDI.
- Dairy: One cup of plain yogurt provides about 50% of the RDI.
- Eggs: One large egg provides 16% of the RDI.
However, keep in mind that these amounts can vary greatly. Iodine is found mostly in the soil and the sea, so if the soil is iodine-poor then the food growing in it will be low in iodine as well.
Some countries have responded to iodine deficiency by adding it to salt, which has successfully reduced the severity of the problem ().
Bottom Line: Iodine is one of the most common nutrient deficiencies in the world. It may cause enlargement of the thyroid gland. Severe iodine deficiency can cause mental retardation and developmental abnormalities in children.
Vitamin D is a fat-soluble vitamin that works like a steroid hormone in the body.
It travels through the bloodstream and into cells, telling them to turn genes on or off.
Almost every cell in the body has a receptor for vitamin D.
Vitamin D is produced out of cholesterol in the skin when it is exposed to sunlight. So people who live far from the equator are highly likely to be deficient, since they have less sun exposure (, ).
In the US, about 42% of people may be vitamin D deficient. This number rises to 74% in the elderly and 82% in people with dark skin, since their skin produces less vitamin D in response to sunlight (, ).
Vitamin D deficiency is not usually visible. The symptoms are subtle and may develop over years or decades (, ).
Adults who are deficient in vitamin D may experience muscle weakness, bone loss and increased risk of fractures. In children, it may cause growth delays and soft bones (rickets) (, , ).
Also, vitamin D deficiency may play a role in reduced immune function and an increased risk of cancer (22).
Unfortunately, very few foods contain significant amounts of this vitamin.
The best dietary sources of vitamin D are (23):
- Cod liver oil: A single tablespoon contains 227% of the RDI.
- Fatty fish, such as salmon, mackerel, sardines or trout: A small, 3-ounce serving of cooked salmon (85 g) contains 75% of the RDI.
- Egg yolks: One large egg yolk contains 7% of the RDI.
People who are truly deficient in vitamin D may want to take a supplement or increase their sun exposure. It is very hard to get sufficient amounts through diet alone.
Bottom Line: Vitamin D deficiency is very common. Symptoms include muscle weakness, bone loss, increased risk of fractures and soft bones in children. It is very difficult to get sufficient amounts from diet alone.
Vitamin B12, also known as cobalamin, is a water-soluble vitamin.
It is essential for blood formation, as well as for brain and nerve function.
Every cell in your body needs B12 to function normally, but the body is unable to produce it. Therefore, we must get it from food or supplements.
Vitamin B12 is only found in animal foods (with the exception of nori seaweed and tempeh — see here). Therefore, people who do not eat animal products are at an increased risk of deficiency.
Studies have shown that vegetarians and vegans are highly likely to be deficient in vitamin B12. Some numbers go as high as 80–90% (, ).
More than 20% of elderly people may also be deficient in vitamin B12, since absorption decreases with age (, , ).
The absorption of vitamin B12 is more complex than the absorption of other vitamins, because it needs help from a protein known as intrinsic factor.
Some people are lacking in this protein, and may therefore need B12 injections or higher doses of supplements.
One common symptom of vitamin B12 deficiency is megaloblastic anemia, which is a blood disorder that enlarges the red blood cells.
Other symptoms include impaired brain function and elevated homocysteine levels, which is a risk factor for several diseases (, ).
Dietary sources of vitamin B12 include:
- Shellfish, especially clams and oysters: A 3-ounce (85 g) portion of cooked clams provides 1400% of the RDI.
- Organ meat: One 2-ounce slice (60 grams) of liver provides more than 1000% of the RDI.
- Meat: A small, 6-ounce beef steak (170 grams) provides 150% the RDI.
- Eggs: Each whole egg provides about 6% of the RDI.
- Milk products: One cup of whole milk provides about 18% of the RDI.
Large amounts of B12 are not considered harmful, because it is often poorly absorbed and excess amounts are expelled via urine.
Bottom Line: Vitamin B12 deficiency is very common, especially in vegetarians and the elderly. The most common symptoms include a blood disorder, impaired brain function and elevated homocysteine levels.
Calcium is essential for every cell. It mineralizes bone and teeth, especially during times of rapid growth. It is also very important for the maintenance of bone.
Additionally, calcium plays a role as a signaling molecule all over the body. Without it, our heart, muscles and nerves would not be able to function.
The calcium concentration in the blood is tightly regulated, and any excess is stored in bones. If there is lack of calcium in the diet, calcium is released from the bones.
That is why the most common symptom of calcium deficiency is osteoporosis, characterized by softer and more fragile bones.
One survey found that in the US, less than 15% of teenage girls and less than 10% of women over 50 met the recommended calcium intake ().
In the same survey, less than 22% of young, teenage boys and men over 50 met the recommended calcium intake from diet alone. Supplement use increased these numbers slightly, but the majority of people were still not getting enough calcium.
Symptoms of more severe dietary calcium deficiency include soft bones (rickets) in children and osteoporosis, especially in the elderly (, ).
Dietary sources of calcium include:
- Boned fish: One can of sardines contains 44% of the RDI.
- Dairy products: One cup of milk contains 35% of the RDI.
- Dark green vegetables, such as kale, spinach, bok choy and broccoli: One ounce of fresh kale provides 5.6% of the RDI.
The effectiveness and safety of calcium supplements have been somewhat debated in the last few years.
Some studies have found an increased risk of heart disease in people taking calcium supplements, although other studies have found no effects (, , ).
Although it is best to get calcium from food rather than supplements, calcium supplements seem to benefit people who are not getting enough in their diet ().
Bottom Line: Low calcium intake is very common, especially in young females and the elderly. The main symptom of calcium deficiency is an increased risk of osteoporosis in old age.
Vitamin A is an essential fat-soluble vitamin. It helps form and maintain healthy skin, teeth, bones and cell membranes.
Furthermore, it produces our eye pigments - which are necessary for vision (38).
There are two different types of dietary vitamin A:
- Preformed vitamin A: This type of vitamin A is found in animal products like meat, fish, poultry and dairy.
- Pro-vitamin A: This type of vitamin A is found in plant-based foods like fruits and vegetables. Beta-carotene, which the body turns into vitamin A, is the most common form.
More than 75% of people who eat a western diet are getting more than enough vitamin A and do not need to worry about deficiency ().
However, vitamin A deficiency is very common in many developing countries. About 44–50% of preschool-aged children in certain regions have vitamin A deficiency. This number is around 30% in Indian women (, ).
Vitamin A deficiency can cause both temporary and permanent eye damage, and may even lead to blindness. In fact, vitamin A deficiency is the world's leading cause of blindness.
Vitamin A deficiency can also suppress immune function and increase mortality, especially among children and pregnant or lactating women ().
Dietary sources of preformed vitamin A include:
- Organ meat: One 2-ounce slice (60 g) of beef liver provides more than 800% the RDI.
- Fish liver oil: One tablespoon contains roughly 500% the RDI.
Dietary sources of beta-carotene (pro-vitamin A) include:
- Sweet potatoes: One medium, 6-ounce boiled sweet potato (170 g) contains 150% of the RDI.
- Carrots: One large carrot provides 75% of the RDI.
- Dark green leafy vegetables: One ounce (28 g) of fresh spinach provides 18% of the RDI.
While it is very important to consume enough vitamin A, it is generally not recommended to consume very large amounts of preformed vitamin A, as it may cause toxicity.
This does not apply to pro-vitamin A, such as beta-carotene. High intake may cause the skin to become slightly orange, but it is not dangerous.
Bottom Line: Vitamin A deficiency is very common in many developing countries. It may cause eye damage and lead to blindness, as well as suppress immune function and increase mortality among women and children.
Magnesium is a key mineral in the body.
It is essential for bone and teeth structure, and is also involved in more than 300 enzyme reactions ().
Almost half of the US population (48%) consumed less than the required amount of magnesium in 2005-2006 ().
Low intake and blood levels of magnesium have been associated with several diseases, including type 2 diabetes, metabolic syndrome, heart disease and osteoporosis (, ).
Low levels of magnesium are particularly common among hospitalized patients. Some studies find that 9–65% of them are magnesium deficient (, , ).
This may be caused by disease, drug use, reduced digestive function or inadequate magnesium intake ().
The main symptoms of severe magnesium deficiency include abnormal heart rhythm, muscle cramps, restless leg syndrome, fatigue and migraines (, , ).
More subtle, long-term symptoms that you may not notice include insulin resistance and high blood pressure.
Dietary sources of magnesium include:
- Whole grains: One cup of oats (6 ounces or 170 g) contains 74% the RDI.
- Nuts: 20 almonds provide 17% of the RDI.
- Dark chocolate: 1 ounce (30 g) of dark chocolate (70–85%) provides 15% of the RDI.
- Leafy, green vegetables: 1 ounce (30 g) of raw spinach provides 6% of the RDI.
Bottom Line: Many people are eating very little magnesium, and deficiency is common in Western countries. Low magnesium intake has been associated with many health conditions and diseases.
It is possible to be deficient in almost every nutrient, but these 7 are by far the most common.
Children, young women, the elderly and vegetarians seem to be at the highest risk of several deficiencies.
The best way to prevent a deficiency is to eat a balanced, real food-based diet that includes nutrient-dense foods (both plants and animals).
However, supplements can be necessary when it is impossible to get enough from the diet alone.