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Common Nutritional Deficiencies, Testing, & Ways to Avoid

Written by Biljana Novkovic, PhD | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Biljana Novkovic, PhD | Last updated:

Even if you eat a healthy diet, you may still fall short of essential vitamins & minerals. Read on to learn about the common nutrient deficiencies & how to avoid them.

What are Nutritional Deficiencies?

You may eat a sufficient amount of food, and perhaps more than you need to. You probably do get your fair share of fruits and vegetables. But there is a good chance you’re not getting enough nutrients.

Sounds a little extreme? Well, according to a study that analyzed 4 popular diet plans, even people who eat five daily servings of fruits and vegetables may not get enough of certain vitamins for optimal health. Most people, for instance, cannot get the healthiest levels of folate and vitamins D and E from recommended diets [1].

Another study found that out of 20 individuals, including both athletes and sedentary people, all of them had at least two or more nutrient deficiencies, the most common being iodine, vitamin D, zinc, calcium, and vitamin E [2].

Why does this happen? Firstly, how and where your food was grown influences its nutritional content. Studies show that the nutritional quality of food has declined over the years due to modern day agricultural practices [2, 3].

And if you are older, have digestive problems, take certain medications, or drink coffee or tea, you likely will absorb fewer nutrients from food [4].

Why does this matter? Because even minor deficiencies of critical vitamins and minerals can have harmful effects. They can damage your DNA, accelerate aging, and increase your risk of becoming overweight and obese [1, 5].

Below is a list of the most common nutritional deficiencies. The good news is that it’s easy to remedy these issues and get yourself back on track towards optimal health!

Common Nutritional Deficiencies

1. Iron

When it comes to common nutritional disorders, iron deficiency takes the cake. WHO (World Health Organization) estimates that iron deficiency affects more than 25% of people worldwide [6, 7, 8]!

You are more likely to have an iron deficiency if you are a woman, due to blood loss during menstruation. Pregnant women and children are also at risk due to their increased need for iron [9].

Iron is found in all of your cells. One of its main roles is to transport oxygen to tissues, as a part of hemoglobin in red blood cells [9].

Iron is required for [10, 11, 12, 13, 14, 15]:

  • Red blood cell production
  • Energy production in the heart and muscles
  • Brain development and normal brain function
  • Immune system development and immune response
  • Resistance to infections
  • Production and degradation of DNA

Given these important roles, it’s not surprising that even a mild iron deficiency can result in anemia, fatigue, headaches, pale skin, anxiety, and shortness of breath [16, 17, 18, 19, 20, 21, 22].

Your doctor can test your iron levels by doing the following blood tests:

  • Iron. Although iron is commonly tested, blood iron may not be the best measure of your overall iron content because it fluctuates. It can increase after an iron-rich meal for example [23, 24]. That is why this test is often run together with TIBC or less commonly UIBC.
  • TIBC (Total iron binding capacity). This test measures the capacity of proteins in the blood, including transferrin, to bind iron. TIBC can be measured together with iron, to give a better indication of iron deficiency.
  • UIBC (Unsaturated iron binding capacity). This test measures the “reserve capacity” of transferrin or the amount of transferrin that has not yet been saturated with iron.
  • Transferrin saturation (% saturation) – is the percentage of transferrin that is saturated with iron. This value is derived from your iron and TIBC levels.
  • Ferritin. This protein is usually a good measure of your body’s total iron stores. However, it can be unreliable if you have an infection, chronic inflammation, liver, kidney, or other diseases [25].

It is important to test your iron levels before you start taking supplements or increase your dietary iron intake. Too much iron can be dangerous, as it can build up in the body and cause cell damage [26]! That’s why you should take iron supplements only after exhausting dietary options and consulting with your doctor!

If your iron levels are suboptimal or low, you can boost your dietary intake by increasing red meat, poultry, fish. Beans, nuts, tempeh, and green leafy vegetables such as broccoli, kale, and spinach are plant sources rich in iron [27].

Avoid milk, caffeine, coffee, and tea during meals, as these can reduce iron absorption. Taking vitamin C with iron-rich foods, on the other hand, increases iron absorption [28, 29, 30, 31, 32, 33, 34, 35].

2. Calcium

Calcium is essential for every cell. Its main function is to support the structure and function of your skeleton. More than 99% of your calcium is stored in your bones and your teeth. The rest is used for other critical processes such as muscle contraction, blood clotting, and the transmission of nerve signals [36].

Even though it’s one of the most vital minerals for your health, many people are still not getting enough calcium in their diet. In fact, one study suggests that nearly 68% of the American population is low in calcium [37].

Calcium deficiency symptoms vary widely – ranging from nonexistent or mild to severe and life-threatening. In some cases, you may experience tingling in the fingers and toes and muscle cramping. Left untreated, calcium deficiency can lead to bone disease (e.g. rickets, osteopenia, and osteoporosis) [38, 39].

If your doctor suspects a calcium deficiency they may test your bone mineral density. A calcium blood test is not a measure of calcium sufficiency, because your blood levels are kept in check even when calcium becomes low.

Thankfully, calcium deficiency is relatively easy to treat. It typically involves adding more calcium to your diet. Calcium-rich foods include green leafy vegetables and dairy products [36].

Foods that bind calcium, such as spinach, potatoes, rhubarb, and beets can reduce calcium absorption, so it’s best to avoid having them with calcium-rich foods, if your calcium levels are low or suboptimal [40].

Your doctor may prescribe a calcium supplement if needed [41].

3. Vitamin B12

Vitamin B12 is often touted as the “energy vitamin” because of its role in energy metabolism. It helps make DNA, nerve and blood cells, and is essential for a healthy brain and immune system [42].

Vitamin B12 is only found in animal products like eggs, meat, shellfish, and dairy. There are estimates that around 14-16% of people don’t get enough B12. People at risk are [43, 44, 45, 46, 47]:

  • Vegetarians or vegans
  • Those suffering from celiac disease or other digestive issues that impair nutrient absorption
  • Seniors, because as we get older, our ability to absorb nutrients decreases

Sometimes, it’s easy to miss a deficiency of vitamin B12 because it can take years before the symptoms appear. As the condition worsens, common symptoms include brain fog, fatigue, apathy, mood swings, memory problems, muscle weakness, and tingling in the arms and legs. That is why it is critical that you get your levels checked before complications occur [48].

You can check your vitamin B12 levels by doing a total vitamin B12 blood tests. You can also test your active vitamin B12 levels. However, this second test is more expensive, and studies show it may not do a better job at scanning for vitamin B12 deficiency compared to a total vitamin B12 test [49, 50].

If your levels are low or suboptimal, you can increase them by consuming more vitamin B12-rich foods or taking supplements. Good sources include red meat, fish, poultry, yogurt, and milk. Vitamin B12 is poorly absorbed from eggs [51, 52, 53].

If needed, your doctor will prescribe vitamin B12 supplements or injections.

Avoid smoking and alcohol. Both decrease vitamin B12 levels [54, 55, 56, 57].

4. Vitamin E

Vitamin E is an important antioxidant that protects your cells from free radicals – byproducts of oxidative stress [58].

It is estimated that one-fifth of the world’s population and at least 75% of Americans are low in vitamin E. Lower vitamin E levels have been associated with a higher risk for depression, heart disease, cognitive decline, and immune dysfunction [59, 60, 61, 62].

You can check your vitamin E levels by doing an alpha-tocopherol and a gamma-tocopherol blood test. These are two major forms of vitamin E.

If you have a deficiency, don’t fret! The solution is simple: eat plenty of vitamin E rich foods. Vitamin E rich foods include [63, 64, 58]:

  • Oils (wheat germ, sunflower, hazelnut, almond, cottonseed, safflower, etc.)
  • Sunflower seeds
  • Almonds
  • Hazelnuts
  • Peanut butter
  • Avocadoes
  • Spinach
  • Broccoli
  • Kiwi

Your gut needs fat to absorb vitamin E, so make sure you consume enough healthy fats in your diet (e.g. olive oil, nuts, avocados) when taking supplements [65].

If needed, your doctor may prescribe a vitamin E supplement.

Opt for a supplement that contains multiple forms of vitamin E (e.g. both alpha-tocopherol, gamma-tocopherol).

Some earlier studies suggested that megadoses of vitamin E supplements may be harmful [66]. However, more recent and larger studies show no negative effects with very high supplement doses [67]. This may depend on underlying conditions, and factors such as smoking.

5. Magnesium

Magnesium is the 4th most abundant mineral in the body. It is required for more than 300 different bodily processes. Because of this, a deficiency can wreak havoc on your health. Your body needs magnesium for [68, 69, 70]:

  • Activating muscles and nerves
  • Energy production
  • Making DNA
  • Activating vitamin D and B-vitamins

An estimated 75% of the U.S. population does not meet the recommended dietary allowance of magnesium [71].

Low levels are marked by loss of appetite, fatigue, nausea, insomnia, irritability, and muscle weakness. In its worst stages, magnesium deficiency can contribute to osteoporosis, heart disease, high blood pressure, and diabetes [72, 73, 74, 75, 76, 69, 77].

Magnesium is another nutrient that is easy to test. Ask your doctor for a magnesium blood test. If your levels are suboptimal or low, increase the intake of magnesium-rich foods or take supplements.

If you’re not including lots of dark green leafy vegetables, avocados, nuts, and seeds in your diet, start right now [78, 79, 80]. Other magnesium-rich foods include:

6. Vitamin D

Studies suggest that around 42% of adults in the U.S. are deficient in the “sunshine vitamin”, vitamin D [83, 84].

Vitamin D helps maintain healthy levels of calcium and phosphorus by increasing their absorption in the gut. In this way, vitamin D is critical for the proper growth and formation of bones [85, 86].

It also plays a role in muscle strength and performance, immune system function, blood pressure, and insulin secretion [86, 87, 88, 89].

Vitamin D is produced by the skin upon exposure to sunlight. It can also be obtained in the diet, or through vitamin supplements [90].

One of the major causes of low vitamin D levels is insufficient exposure to UVB radiation from the sun, which prevents the skin from being able to produce enough vitamin D. Specific risk factors include:

  • Living at high latitudes (>37°) [91, 92, 93]
  • Living in regions where there are large seasonal changes in sun exposure [94]
  • Living in areas with high levels of air pollution, which blocks out sunlight [95]
  • Over-use of sunscreen [96]
  • Having darker skin [97, 98]
  • Keeping the skin covered up (in colder climates or certain cultures) [99, 100]

Symptoms of vitamin D deficiency are not always obvious and can take years to manifest. Some signs may include fatigue, muscle weakness, bone loss, and depression [101].

If you are experiencing any of these symptoms, you should ask your doctor to test your vitamin D levels (25-hydroxyvitamin D).

High doses of vitamin D supplements can be toxic, so it’s important for you and your doctor to keep track of your levels if you choose to supplement.

Getting enough vitamin D from food can be tricky – cod liver, fatty fish such as salmon and sardines, egg yolk, and mushrooms are the only good natural sources. However, a lot of other foods are now fortified with this vitamin. If supplementing, choose vitamin D3 (cholecalciferol), the form your body naturally makes when it’s exposed to sunlight [102, 103, 104].

7. Zinc

Zinc is an essential mineral found in all organs, tissues, and fluids in the body [105].

As the second most abundant trace mineral in the body after iron, it plays a crucial role in a variety of biological processes [106, 107].

Zinc is required for the activity of more than 300 enzymes involved in the metabolism of carbohydrates, fats, proteins, and nucleic acids [108].

It also plays roles in immune function, wound healing, blood clotting, thyroid function, vision, taste, and smell. It’s also needed to make testosterone [109].

Given zinc’s many key roles, it’s alarming that, according to research, around 31% of the world’s population may be deficient in this mineral [110]

You are at risk for zinc deficiency if you [111, 112]:

  • have digestive disorders
  • are vegetarian
  • are pregnant and lactating
  • are an alcoholic
  • have sickle cell disease

Because zinc plays such critical roles in your body, symptoms of a deficiency can show up in a variety of ways. Some of the more common symptoms include diarrhea, infections, hair loss, eye and skin conditions, delayed wound healing, impotence, and loss of appetite [113].

If you suspect that you have a zinc deficiency, your doctor can check your levels by ordering a blood or urine test.

Your doctor may prescribe zinc supplements if you’re deficient. Good dietary sources of zinc include red meats, seafood, dairy products, nuts, legumes, and whole grains [114].

8. Iodine

Do you suffer from dry mouth, dry skin, an enlarged thyroid gland, rapid heart rate, shortness of breath, and weight gain? These are all symptoms of iodine deficiency [115, 116, 117, 118].

There are estimates that approximately one-third of the world’s population is iodine deficient [119, 120, 121].

Iodine is an essential mineral found in all of your organs and tissues. Your body needs iodine for normal thyroid function, including the production of thyroid hormones, which support brain development, bone maintenance, growth and metabolism [116, 122].

The easiest way to check your iodine levels is to do a urine iodine test. This test measures your recent iodine intake. For chronic iodine deficiency (or overload) it is useful to also check your thyroid function (e.g. TSH, free T4, free T3).

Work with your doctor to find out if your iodine levels are low.

Foods rich in iodine include eggs, fish, meat, cereals, green vegetables, spinach, and seaweed (kelp, kombu, nori, and wakame) [123, 115].

You can also use more iodized salt to season your food (unless you have to restrict the amount of salt in your diet for health reasons) [124].

Iodine supplements should only be used under medical supervision! Because of the potentially serious risks associated with excess iodine you and your doctor need to monitor your iodine levels and thyroid function while supplementing [125].


Your doctor will interpret your lab results taking into account your medical history, symptoms, and other test results. Nutritional deficiencies are often due to underlying causes that cannot be corrected by simple dietary changes. That’s why it’s important to work with your doctor to find out what’s causing your low nutrient levels and to treat any underlying conditions!

About the Author

Biljana Novkovic

Biljana Novkovic

Biljana received her PhD from Hokkaido University.
Before joining SelfHacked, she was a research scientist with extensive field and laboratory experience. She spent 4 years reviewing the scientific literature on supplements, lab tests and other areas of health sciences. She is passionate about releasing the most accurate science and health information available on topics, and she's meticulous when writing and reviewing articles to make sure the science is sound. She believes that SelfHacked has the best science that is also layperson-friendly on the web.


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