Micronutrient Deficiencies, How to Know If You Have Them and What to Do to Address Them?

Co-written by Erica Gittleson, RD and Dr. Bojana Jankovic Weatherly.

Vitamins and minerals are micronutrients required by the body to carry out a range of normal functions, from helping us fight infections, to supporting normal growth and development, hormonal balance and supporting our organs to function normally. We acquire these micronutrients from foods we eat because the body does not produce essential minerals. Similarly, we rely on getting most of our vitamins from food, because the body either does not produce them, or produces them in very small quantities. A nutrient deficiency can occur when this nutrient is not consumed in adequate amounts, when the body doesn’t absorb the necessary amount of a nutrient from diet or when there is excess loss (e.g., blood loss with monthly cycles). Some common nutrient deficiencies include iron deficiency (especially in biological females of reproductive age), vitamin B12 deficiency (especially in people who are vegan or vegetarian and not supplementing with vitamin B12, individuals with Crohn’s disease, and individuals who have had gastric bypass surgery), and vitamin D deficiency. Vitamin deficiencies can have serious consequences ranging from impaired cognition, fatigue, depression, neuropathy, increased risk of cardiovascular disease, eye disease, infections, or cancer. Vitamin D deficiency has been correlated with a greater incidence of diabetes, increased susceptibility to viral infections, increased risk of inflammation and osteoporosis.

How to Prevent Nutrient Deficiencies

It’s important to prevent deficiencies right in their tracks. How do we do this? To prevent or identify deficiencies, it’s important to acknowledge common risk factors for specific nutrient deficiencies, signs and symptoms, and to ask your doctor or qualified healthcare provider to test you for potential nutrient deficiencies you may be at risk for, or exhibiting symptoms of. Some warning signs to watch out for, include: low energy, depressed mood, trouble concentrating, recurrent viral infections, poor wound healing, neuropathy (this can present as numbness or tingling), or anemia. In this article, we will review common nutrient deficiencies, their possible causes, and best ways to prevent them (1).

Nutrient Deficiencies, Causes, Manifestations, Diagnosis and Treatment

1. Vitamin D Deficiency (can lead to bone loss, causing osteoporosis)

Vitamin D deficiency is extremely common, affecting approximately 42% of the U.S. population, according to research published in the National Institutes of Health database. While vitamin D deficiency may not present with any obvious signs or symptoms, you may have vitamin D deficiency if you experience the following signs or symptoms (18):

• Osteoporosis
• Fatigue
• Depression
• Increased susceptibility to viral infections
• Increased risk of inflammation
• Impaired blood glucose and increased risk of diabetes
• Poor wound healing
• Bone pain

The epidermal layer of the skin synthesizes vitamin D when exposed to UV radiation. In the presence of sunlight, a form of vitamin D 3 called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin) in the kidneys. Vitamin D is essential for normal absorption of calcium and phosphorus, which are required for healthy bones (29). Risk factors for vitamin D deficiency include inadequate exposure to sunlight, having dark skin, having inflammatory bowel disease or other gastrointestinal conditions that cause malabsorption (19).

Vegans and vegetarians may also be at high risk as most of the natural food sources of vitamin D are fish, dairy, and poultry.

Adding the right foods to your diet, regular (but safe!) exposure to morning sun, and supplementation, as needed are the best ways to prevent vitamin D deficiency.

The RDA of vitamin D is 600 IU/day for men and women aged 19-70 and 800IU for men and women ages 70+. Three ounces of cooked salmon contain 447 IU of vitamin D, which meets 112% of the daily requirement. Three ounces of canned tuna fish contains 154 IU of the vitamin and meets 39% of the daily requirement (19). Other good sources include milk, yogurt, eggs, beef liver, vitamin d fortified soy and almond milk, vitamin d fortified cereals, mushrooms, and sunshine!

Vitamin D deficiency can lead to issues with your bones and muscles, it also plays a role in your nervous system, musculoskeletal system and immune system. Deficiency most commonly affects people over the age of 65 and people who have darker skin. According to the National Institute of Health, vitamin D levels of 50 nmol/L (20 ng/mL) or above are sufficient for most people for bone and overall health. Levels below 30 nmol/L (12 ng/mL) are too low and might weaken your bones and affect your health (36). The Endocrine Society considers 40 to 60 ng/mL to be the optimal range. Many integrative and functional medicine practitioners aim for similar, higher ranges to support various systems and conditions impacted by vitamin D deficiency such as autoimmune conditions, infections, metabolic disorders and cancer.

In our clinical experience, vitamin D deficiency is the most common vitamin deficiency we find when we review lab tests with our patients. Oftentimes, the doses of supplementation required to reach optimal vitamin D levels are higher than what is recommended by the Institute of Medicine. That being said, over-supplementation with vitamin D can have risks of hypercalcemia, and it is important to adequately monitor levels while on supplementation.

2. Iron Deficiency (can lead to iron-deficiency anemia)

The prevalence of iron deficiency anemia in the US is 2% in adult men, 9 to 12% in non- Hispanic white women, and nearly 20% in black and Mexican-American women (27). Common symptoms of iron deficiency anemia include the following symptoms (3):

• Pale skin
• Extreme fatigue
• Brittle nails
• Chest pain and shortness of breath (accompanied by fast heartbeat)
• Cold hands and feet
• Tongue inflammation
• Unusual cravings for non-nutritive substances like ice or dirt
• Headache and dizziness

When your body doesn’t have enough iron to produce hemoglobin, you can develop iron deficiency anemia. Blood loss is one major cause of iron deficiency and biological women of reproductive age are at a higher risk as they lose blood during menstruation. That being said, a lack of iron in your diet can lead to this deficiency.

If you have Celiac disease, your body can also become deficient in iron as Celiac disease affects the intestine’s ability to absorb nutrients from food, including iron (2).

Other populations at risk for iron deficiency are vegetarians or vegans and individuals who donate blood more frequently (3).

The RDA (recommended dietary allowance) of iron for women ages 31-50yo is 18yo mg/day and 8mg/day for women ages 51yo+. For men ages 31yo+ the RDA is 8 mg/day (1).

The best modes of treatment include taking iron supplements and enriching your diet with foods rich in iron. Other methods include intravenous iron or red blood cell transfusions, which are used during severe cases of iron deficiency anemia.

The richest sources of heme iron are lean meat and seafood. Heme iron is the form of iron found in meat, poultry, and seafood – and is more easily absorbed in the body (4).

Sources of non-heme iron include nuts, beans, and vegetables (especially spinach) (3). One serving of fortified breakfast cereals contain about 18 milligrams of iron, which meets 100% of the daily requirement. Three ounces of pan-fried beef liver contains 5 milligrams of iron, which meets 28% of the daily requirement. Half a cup of boiled spinach contains 3 milligrams of iron, meeting 17% of the daily requirement (5).

3. B Vitamin Deficiencies

A deficiency of vitamin B1, or thiamin, can cause beriberi. Beriberi is characterized by impaired sensory, reflex, and motor functions. It may also lead to congestive heart failure, causing edema in the lower limbs, and in certain cases, even death (10). Individuals who consume alcohol, have diabetes, older adults, and those who have undergone bariatric surgery are at a higher risk. This type of deficiency is rare as most people meet the RDA through their diets.

The signs and symptoms of riboflavin deficiency include skin disorders, hyperemia (excess blood in vessels supplying an organ), edema of the mouth and throat, angular stomatitis (lesions at the corners of the mouth), cheilosis (swollen, cracked lips), hair loss, reproductive problems, sore throat, itchy and red eyes, and degeneration of the liver and nervous system. It’s important to note that riboflavin might play a role in migraine headaches. Mitochondrial dysfunction is thought to play a role in some types of migraines – and because riboflavin is required for mitochondrial function, researchers are studying the potential use of riboflavin to prevent or treat migraine headaches (37). In clinical practice, this is often recommended to people with migraines.

A deficiency of vitamin B3, or niacin, causes pellagra. This condition is characterized by diarrhea, dementia, and sun-sensitive dermatitis. If left untreated, pellagra can lead to death (11). This type of deficiency is also rare as it’s well absorbed through most foods.

A deficiency of vitamin B7, or biotin, causes thinning of hair and rashes around the eyes, nose, and mouth. It may also cause skin infections and, in rare cases, seizures (12). Vitamin B7 deficiency is also rare as most people get enough through a varied diet.

Deficiency of vitamin B12 (also called cobalamin) can cause tiredness, loss of appetite, weight loss, constipation, and neuropathy. Other symptoms can include depression and confusion (13). This is the most common vitamin B deficiency we see in our practice. In the United States, approximately 6% of adults younger than 60 years have vitamin B12 deficiency, but the rate is closer to 20% in those older than 60 (28). Individuals with Crohn’s disease, small intestinal bacterial overgrowth (SIBO), individuals who have had gastric bypass surgery, individuals on metformin, and those consuming a vegan or vegetarian diet may be at risk of vitamin B12 deficiency.

Folate, or B9, is another B vitamin whose deficiency can cause serious complications. Symptoms can include weakness, difficulty in concentrating, and shortness of breath. It can also lead to gastrointestinal issues (14). A folate deficiency is rare because it is found in a wide range of foods.

In pregnant women, folate deficiency increases the risk of giving birth to infants with neural tube defects. Inadequate maternal folate status can also cause low infant birth weight, preterm delivery, and retardation of fetal growth (14). This is why it is important to take folate during pregnancy, and ideally, in the months leading up to pregnancy.

Individuals with alcoholism are at risk of folate deficiency as well.

Foods rich in B vitamins include fortified cereals, pork chops, lean beef, tuna, eggs, and boiled spinach (10). The RDA of B1(thiamin) is 1.1mcg/day for women and 1.2mcg/day for men. The RDA of B3 (niacin) is 14mcg/day for women and 16mcg/day for men. The RDA of B7 (biotin) is 30mcg/day for men and women. The RDA of Vitamin B12 (cobalamin) is 2.4mcg/day for men and women. Lastly, the RDA of Folate is 400mcg/day for men and women and at least 600mcg/day for women who are pregnant or planning to become pregnant. Note: for those with the MTHFR gene mutation it’s important to supplement with methylated folate as their bodies cannot utilize folate properly.

4. Vitamin A Deficiency (causes night blindness)

You may have vitamin A deficiency if you experience the following symptoms (8):

• Dry eyes
• Dry and scaly skin
• Dry hair
• A cloudy cornea (loss of transparency of the cornea)
• Night blindness

Vitamin A deficiency in the US is rare. Lack of adequate dietary intake is the biggest cause of vitamin A deficiency. Certain health conditions like Celiac disease, chronic diarrhea, cystic fibrosis, and cirrhosis can interfere with the absorption of vitamin A in the body (8).

Infants, children, pregnant and lactating women are at a higher risk of developing vitamin A deficiency. (9).

Oral vitamin A could be a promising way of treating the deficiency, especially if the symptoms are severe or malabsorption is the cause. These may also include beta- carotene supplements. However, it’s important to keep in mind that beta-carotene supplements have been associated with an increased risk of certain cancers (8). Studies have shown that supplementation with beta-carotene increases the risk of lung cancer and gastric cancer in smokers and asbestos workers.

The RDA for vitamin A for women is 700 mcg (2333 IU)/day and 900 mcg (3000iu) /day for men. Sweet potato is the richest natural source of vitamin A. One whole baked sweet potato contains 28,058 IU of vitamin A, which meets a whopping 561% of the daily requirement.

Beef liver is another great source – 3 ounces of pan-fried liver offers 22,175 IU of vitamin A, meeting 444% of the daily requirement (9). Half a cup of boiled spinach offers 11,458 IU of vitamin A, and this meets 229% of the daily requirement (9).

5. Magnesium Deficiency

According to World Health Organization statistics, as much as 75% of the U.S. adult population does not meet the U.S. Food and Drug Administration’s Recommended Daily Intake of Magnesium. You may have magnesium deficiency if you experience the following symptoms (23):

• Vomiting
• Nausea
• Fatigue
• Weakness
• Loss of appetite
• Numbness
• Seizures
• Abnormal heart rhythm
• Tingling
• Muscle cramps

The primary causes of magnesium deficiency are dietary inadequacy or malabsorption. Excess alcohol intake and prolonged diarrhea may also cause magnesium deficiency (24).

People at high risk for magnesium deficiency include those who are addicted to alcohol, individuals with diabetes, gastrointestinal issues, and older adults (23).

Taking magnesium orally is the most common form of treatment (24).

Severe magnesium deficiency may also lead to the deficiency of calcium or potassium (given the disruption of mineral homeostasis), leading to further problems (23).

Including foods rich in magnesium in your diet is the best way to prevent this deficiency. The RDA of magnesium for women ages 19-30 is 310 mg/day and 320 mg/day for women 31-70 years old. The RDA of magnesium for men ages 19-30 is 400 mg/day and 420 mg/day for men ages 31-70. Nuts are among the richest sources of magnesium. One ounce of dry roasted almonds contains 80 milligrams of magnesium, meeting 20% of the daily requirement. A similar quantity of dry roasted cashews contains 74 milligrams of magnesium, meeting 19% of the daily requirement (23). Other sources include spinach, peanuts, and brown rice.

6. Iodine Deficiency (causes goiter and hypothyroidism)

According to the national institute of health, the general U.S. population has adequate iodine intake but some pregnant women may be at risk for iodine deficiency (30). You may have iodine deficiency if you experience the following symptoms (6):

• Goiter, characterizing an enlarged thyroid gland
• Fatigue
• Constipation
• Puffy face
• Muscle weakness
• Dry skin
• Muscle aches and tenderness
• Thinning hair
• Depression
• Impaired memory
• Weight gain
• Increased sensitivity to cold
• Irregular menstrual periods
• Elevated blood cholesterol levels

Iodine deficiency happens when you don’t consume enough iodine through your diet. Iodine is necessary for making thyroid hormone, therefore low iodine is commonly linked to hypothyroidism. Women are more likely to develop hypothyroidism than men. Pregnant women and women, in general, are more likely to be deficient in iodine (6).

The best way to prevent iodine deficiency is to consume foods rich in the nutrient. The RDA of iodine for men and non-pregnant women is 150 mcg/day. For pregnant and lactating women, RDA is 220 mcg/day and 290 mcg/day, respectively.  On a large scale, salt and bread have been fortified with iodine. Iodine supplements are available but it’s important you consult your healthcare provider before starting an iodine supplement (or any supplement).   

Seaweed is the richest source of iodine. Just 1 gram of seaweed contains 16 to 1,984 mcg of iodine, meeting 11% to 1,989% of the daily requirement. Three ounces of baked cod contains 99 mcg of iodine, which meets 66% of the daily requirement. One cup of plain low-fat yogurt contains 75 mcg of iodine, meeting 50% of the daily requirement of the nutrient (7). There is no FDA approved way to test for iodine due to lack of reliability and daily variation in iodine intake.. The most reliable test in population settings to determine iodine deficiency is a urine iodine test.

7. Vitamin C Deficiency (causes scurvy)

Vitamin C is an essential nutrient that must be consumed regularly to prevent deficiency.  While vitamin C deficiency is relatively rare in developed countries due to the availability of fresh produce and the addition of vitamin C to certain foods and supplements, it still affects roughly 7% of adults in the US (31).  You may have vitamin C deficiency if you experience the following symptoms (15):

• Depression
• Fatigue
• Rashes
• Impaired wound healing
• Gingivitis
• Weight loss
• Irritability
• Scurvy (characterized by bleeding gums and opening of previously healed wounds)

The primary cause of scurvy is inadequate intake of vitamin C. Individuals at high risk include people who are addicted to alcohol and smoking, those with a poor diet, and those having severe mental illness. 

Treatment usually involves a high dose of vitamin C administration (16).  Replenishing your diet with foods rich in vitamin C also helps.  The RDA of vitamin C is 75 mg/day for women and 90 mg/day for men.  A ¾ cup of orange juice contains 93 mg of vitamin C, meeting 155% of the daily requirement. A medium orange contains about 70 mg of the vitamin, meeting 117% of the daily requirement (17). Other sources include broccoli, potatoes, and cauliflower. 

8. Calcium Deficiency 

According to the Dietary Guidelines for Americans 2020-2025, nearly 30 percent of adult men and 60 percent of adult women do not consume enough calcium.  Below are common symptoms of calcium deficiency (20):

• Confusion
• Fatigue
• Anxiety
• Brittle nails
• Impaired concentration
• Poor memory
• Dry skin
• Coarse hair
• Alopecia
• Muscle cramps and muscle weakness

Hypocalcemia may be caused by several factors. These include inadequate calcium in the diet, lack of sunlight exposure, chronic kidney disease, liver disease or liver cirrhosis, and reduced intestinal absorption of calcium (20). Vitamin D deficiency can also lead to hypocalcemia (21).

Individuals at risk of calcium deficiency include postmenopausal women, individuals with lactose intolerance, and vegetarians (21). Treatment for hypocalcemia usually involves oral calcium and vitamin D in the form of supplements (22).

The RDA of calcium is 1000 mg/day for men and women ages 31-50 and 1200 mg/day for men and women ages 51+. Plain, low-fat yogurt is the richest source of calcium. Eight ounces of the yogurt contains 415 milligrams of calcium, meeting 42% of the daily requirement. Eight ounces of nonfat milk contains 299 milligrams of calcium, meeting 30% of the daily requirement (22).  Non-dairy sources of calcium include:  fortified cereals, sardines, salmon, tofu, spinach and collard greens.  

9. Zinc Deficiency

Most people in the United States consume adequate amounts of zinc, however, it’s estimated that as many as 40 percent of elderly experience deficiency due to inadequate dietary intake and decreased absorption (32). You may have zinc deficiency if you experience the following symptoms (25):

• Loss of appetite
• Weakened immune system
• Hair loss
• Diarrhea
• Lethargy
• Slow wound healing
• Unexplained weight loss

Alcoholism is a major cause of zinc deficiency. Other causes include chronic kidney disease, diabetes, liver or pancreas disorders, and sickle cell disease (25).

Individuals at a higher risk include those addicted to alcohol, vegetarians, individuals with gastrointestinal issues, older adults, and pregnant or lactating women (26).

Treatment for zinc deficiency may involve the intake of zinc supplements. Consuming zinc rich foods works well too.  

The RDA of zinc is 8 mg/day for women and 11 mg/day for men.  Oysters are the richest sources of zinc. Three ounces of cooked oysters contains 74 milligrams of zinc, meeting 493% of the daily requirement. Three ounces of cooked crab contains about 6.5 grams of zinc, which meets 43% of the daily requirement. Baked beans and pumpkin seeds are also excellent sources (26).

10.  Omega 3 Fatty Acid Deficiency

Omega 3 fatty acids are a type of polyunsaturated fatty acid (PUFA) and an important component of cell membranes. Your body needs them to produce signaling molecules called eicosanoids, which help your immune, pulmonary, cardiovascular, and endocrine systems work properly. New research has found that over 68% of adults in the United States do not consume enough omega-3s to meet nutritional needs based on the US Dietary Guidelines (33).  

Few studies have investigated the signs and symptoms of omega-3 deficiency specifically.  To gain a clearer understanding of this topic, scientists need to do more research on the signs and symptoms of omega-3 deficiency specifically, and researchers may need to develop better tests to identify it (34).  The following are potential consequences of low omega-3 fatty acids and high omega-6/omega-3 fatty acid ratio: 

• Skin irritation and dryness
• Depression 
• Dry eyes
• Joint pain and stiffness
• Hair changes (including loss or thinning) 
• Higher risk of cardiovascular disease and autoimmune conditions

The best way to reap the benefits of omega-3 fatty acids is by eating (low mercury) fatty fish at least twice per week, but if you don’t eat fatty fish often, you should consider taking a supplement. It’s important to make sure your supplement contains enough eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These are the most useful types of omega-3 fats, and they are found in fatty fish and algae.  You can also get omega-3 from seeds and nuts, like flax seeds and walnuts. These foods contain alpha-linolenic acid (ALA), which can be partially converted into EPA and DHA in your body (34). Up to 10% of ALA  gets converted to EPA and up to 5% to DHA, so this is a much less efficient way to get these nutrients (38).   

There is no official recommended daily allowance for EPA and DHA. However, most health organizations agree that 250–500 mg of combined EPA and DHA is enough for adults to maintain their overall health. Therapeutic doses are typically higher and on the order of 2g/day. Omega 3 fatty acid supplementation may reduce the risk of heart disease, and may improve symptoms of depression, anxiety and eczema, and in these instances, the supplemental doses would typically be higher. 

The typical Western diet contains 15-17 times more omega-6s than omega-3s. These omega-6 fatty acids come mainly from refined vegetable oils that are added to processed foods. While having some omega 6’s is essential, having excess is proinflammatory. Our ancestors’ omega-6 to omega-3 ratio is believed to have been 1:1. Optimal ratio is considered to be between 2:1 and 5:1, depending upon the condition studied. Omega-6s and omega-3s compete for the same enzymes, which convert the fatty acids into their biologically active forms. Therefore, if you wish to improve your omega-3 status, you should not only be sure to get enough omega-3 from your diet and supplements but also consider reducing your intake of vegetable oils high in omega-6 (34). There is currently no standard test to diagnose an omega-3 deficiency, though there are several ways to analyze omega-3 levels. One way is to measure  individual omega-3s in plasma or serum phospholipids and express them as the percentage of total phospholipid fatty acids by weight. Another way is to assess omega-3 status via analysis of erythrocyte fatty acids, a measurement that reflects longer-term intakes over approximately the previous 120 days. The “omega-3 index” proposed by Harris and von Schacky reflects the content of EPA plus DHA in erythrocyte membranes expressed as a percentage of total erythrocyte fatty acids (35).  

Nutritional deficiencies, if ignored, can lead to chronic diseases, or life-threatening complications. Therefore, we must take good care of ourselves, listen to the signals from our body, and nourish our bodies with a variety of foods.  If you believe you’re at risk for nutrient deficiencies it’s important to work with your doctor, registered dietitian, certified nutrition specialist and/or other qualified healthcare practitioner to ensure appropriate evaluation and testing, nutritional optimization and appropriate supplemental support, if needed. 

For a comprehensive nutritional evaluation, you may reach out to our office to see Dr. Bojana Jankovic Weatherly, MD and Erica Gittleson, RD, who can guide you from a comprehensive assessment, through the diagnostic work up, and offer an evidence-based plan to optimize your nutrients, customized to your needs.

References: 

1. Vitamins and minerals. The Nutrition Source. (2022, September 15). Retrieved November 29, 2022, from https://www.hsph.harvard.edu/nutritionsource/vitamins/ 

2. Freeman H. J. (2015). Iron deficiency anemia in celiac disease. World journal of gastroenterology, 21(31), 9233–9238. https://doi.org/10.3748/wjg.v21.i31.9233

3. U.S. Department of Health and Human Services. (n.d.). Iron-deficiency anemia. National Heart Lung and Blood Institute. Retrieved November 29, 2022, from https://www.nhlbi.nih.gov/health/anemia/iron-deficiency-anemia 

4. Uzel, C., & Conrad, M. E. (1998). Absorption of heme iron. Seminars in hematology, 35(1), 27–34.

5. U.S. Department of Health and Human Services. (n.d.). Office of dietary supplements – iron. NIH Office of Dietary Supplements. Retrieved November 29, 2022, from https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/#h3 

6. U.S. Department of Health and Human Services. (n.d.). Hypothyroidism (underactive thyroid). National Institute of Diabetes and Digestive and Kidney Diseases. Retrieved November 29, 2022, from https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism 

7. U.S. Department of Health and Human Services. (n.d.). Office of dietary supplements – iodine. NIH Office of Dietary Supplements. Retrieved November 29, 2022, from https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/ 

8. Johnson, L. E. (2022, November 18). Vitamin A Deficiency. Merck Manuals Professional Edition. https://www.merckmanuals.com/professional/nutritional-disorders/vitamin-deficiency,-dependency,-and-toxicity/vitamin-a-deficiency

9. Office of Dietary Supplements – Vitamin A and Carotenoids. (n.d.). https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/

10. Office of Dietary Supplements – Thiamin. (n.d.). https://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/

11. Niacin. (2022, January 4). Linus Pauling Institute. https://lpi.oregonstate.edu/mic/vitamins/niacin

12. Office of Dietary Supplements – Biotin. (n.d.). https://ods.od.nih.gov/factsheets/Biotin-Consumer/

13. Office of Dietary Supplements – Vitamin B12. (n.d.). https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/

14. Office of Dietary Supplements – Folate. (n.d.). https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/

15. Johnson, L. E. (2022b, November 18). Vitamin C Deficiency. Merck Manuals Professional Edition. https://www.merckmanuals.com/professional/nutritional-disorders/vitamin-deficiency,-dependency,-and-toxicity/vitamin-c-deficiency

16. NCBI – WWW (n.d.). https://www.ncbi.nlm.nih.gov/books/NBK493187/

17. Office of Dietary Supplements – Vitamin C. (n.d.). https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/

18. Kennel, K. A., Drake, M. T., & Hurley, D. L. (2010). Vitamin D deficiency in adults: when to test and how to treat. Mayo Clinic proceedings, 85(8), 752–758. https://doi.org/10.4065/mcp.2010.0138

19. Office of Dietary Supplements – Vitamin D. (n.d.). https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

20. Schafer AL, Shoback DM. Hypocalcemia: Diagnosis and Treatment. [Updated 2016 Jan 3]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279022/

21.  Office of Dietary Supplements – Vitamin D. (n.d.). https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

22. Lewis, J. L., III. (2022, November 18). Hypocalcemia. Merck Manuals Professional Edition.https://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/electrolyte-disorders/hypocalcemia

23. Office of Dietary Supplements – Magnesium. (n.d.). https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/

24.https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/electrolyte-balance/hypomagnesemia-low-level-of-magnesium-in-the-blood

25. NCBI – Zinc Deficiency (n.d.-c). https://www.ncbi.nlm.nih.gov/books/NBK493231/

26. Office of Dietary Supplements – Zinc. (n.d.). https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/

27.  Killip, S. (2007, March 1). Iron Deficiency Anemia. AAFP. https://www.aafp.org/pubs/afp/issues/2007/0301/p671.html

28.  Allen L. H. (2009). How common is vitamin B-12 deficiency?. The American journal of clinical nutrition, 89(2), 693S–6S. https://doi.org/10.3945/ajcn.2008.26947A

29.  Lumen Learning. (n.d.). Vitamin D Synthesis | Biology for Majors II. https://courses.lumenlearning.com/wm-biology2/chapter/vitamin-d-synthesis/

30. Office of Dietary Supplements – Iodine. (n.d.). https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/

31. Julson, M. E. S. (2018, May 25). 15 Signs and Symptoms of Vitamin C Deficiency. Healthline. https://www.healthline.com/nutrition/vitamin-c-deficiency-symptoms

32. Office of Dietary Supplements – Zinc. (n.d.). https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/

33.  nutraingredients-usa.com. (2021, May 24). Study finds most Americans low in omega-3 fatty acids, could impact mood.https://www.nutraingredients-usa.com/Article/2021/05/24/Study-finds-most-Americans-low-in-omega-3-fatty-acids-could-impact-mood

34.  Hjalmarsdottir, M. F. S. (2022, October 14). How Much Omega-3 Should You Take per Day? Healthline. https://www.healthline.com/nutrition/how-much-omega-3

35.  Office of Dietary Supplements – Omega-3 Fatty Acids. (n.d.). https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/

36. Office of Dietary Supplements – Vitamin D. (n.d.). https://ods.od.nih.gov/factsheets/VitaminD-Consumer/

37.  Office of Dietary Supplements – Riboflavin. (n.d.). https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/

38.  Hjalmarsdottir, F. (2019, May 27). The 3 most important types of omega-3 fatty acids. Healthline. Retrieved March 6, 2023, from https://www.healthline.com/nutrition/3-types-of-omega-3#TOC_TITLE_HDR_6 39. Schlichte MJ, Vandersall A, Katta R. Diet and eczema: a review of dietary supplements for the treatment of atopic dermatitis. Dermatol Pract Concept. 2016 Jul 31;6(3):23-9. doi: 10.5826/dpc.0603a06. PMID: 27648380; PMCID: PMC5006549.