Dietitian Blog, Health/Wellness, MNT Guidelines, Patient Blog | Mar 21 2022

Understanding common vitamin deficiencies

Young woman reading vitamin supplement bottle during breakfast

With a wide variety in individual diets, a key part of the registered dietitian’s nutrition assessment is determining any area of vitamin deficiency and if supplementation should be recommended. Vitamins are needed for numerous processes in the body associated with health and metabolism. Over the last several decades, changes in the way foods are grown and processed have modified the availability of certain nutrients in the diet. In some cases, this may result in a vitamin deficiency.

In the United States, vitamins D, C, B12, B6 and folate are recognized as five of the more common vitamin deficiencies. For a quick refresher on each of these vitamins, daily recommendations and symptoms of a possible deficiency, we have you covered with this quick reference.

Vitamin D

Vitamin D1,2 has several critical roles in the body including support of bones, muscles, the brain and the immune system. This fat-soluble vitamin is unique in that it is produced in the skin from the sun but can also be provided from certain foods and supplements. Experts estimate up to 50% of individuals in the United States have vitamin D insufficiency.

Recommended dietary allowance (RDA):

  • Adults (up to 70 years): 600 IU
  • Adults (71+ years): 800 IU

            *Supplementation may vary depending on individual need

Causes of deficiency: Older age, lack of sun exposure, darker skin color, gastrointestinal (GI) disease with malabsorption, obesity, liver or kidney disease

Clinical signs of deficiency: fatigue, weakness, bone pain, dental caries

Food sources: Fortified milk, juice and cereal, salmon, mackerel, sardines

Vitamin C

Vitamin C2,3, or ascorbic acid, has many roles in the body, including controlling inflammation, and healing and forming blood vessels, muscles, and bone collagen. This vitamin is also linked with absorbing and storing iron. Inadequate dietary vitamin C over time can result in a deficiency of this nutrient.

RDA:  Adults (19+ years): 75 to 90 mg 

            *Avoid long-term supplementation of 2,000 mg or more

Causes of deficiency: Smoking or smoke exposure, GI disorders, limited intake of fruits and vegetables

Clinical signs of deficiency: Weakness, gingivitis, petechiae, poor wound healing, corkscrew hair, splinter hemorrhage

Food sources: Citrus fruit, berries, spinach, potatoes, and broccoli

Vitamin B12

Vitamin B12,2,4 also known as cobalamin, supports the body’s processes with red blood cell creation, metabolism of cells, and function of the nerves. In most cases, vitamin B12 can be consumed easily to meet the RDA, but with certain conditions, a deficiency may occur.

RDA:  Adults (19+ years): 2.4 mcg

Causes of deficiency: GI surgery or malabsorption, certain medications, reduced dietary intake (vegetarianism or veganism)

Clinical signs of deficiency: Pernicious anemia, fatigue, glossitis, hand/foot numbness or tingling, ataxia, bruising, skin hyperpigmentation

Food sources: Poultry, meat, fish, dairy, fortified cereal

Vitamin B6

Vitamin B6,2,5 recognized as pyridoxine, is a co-enzyme for many functions of the brain, nervous, and immune systems. Research remains ongoing but this water-soluble vitamin has been positively linked with cardiovascular disease and pregnancy-associated morning sickness.


  • Adults (19 to 50 years): 1.3 mg
  • Women (51+ years): 1.5 mg
  • Men (51+ years): 1.7 mg

Causes of deficiency: Kidney disease, GI conditions with malabsorption, autoimmune disorders, certain medications, alcoholism

Clinical signs of deficiency: Anemia, dermatitis, depression, glossitis, peripheral neuropathy

Food sources: Chickpeas, salmon, beef liver, tuna, chicken, potatoes, fortified breakfast cereal


Folate2,6,7 requirements are most often met through dietary intake (folate) or from supplements (folic acid). This vitamin is routinely recognized for its need during pregnancy but is also a component of the building of red blood cells and other cell functions.


  • Adults (19+ years): 400 mcg dietary folate equivalents
  • Pregnancy and lactation: 400 to 500 mcg dietary folate equivalents

Causes of deficiency: GI conditions causing malabsorption, poor dietary intake, alcoholism

Clinical signs of deficiency: Neural tube birth defects, tongue and mouth ulcerations, diarrhea, fatigue, peripheral neuropathy, pale conjunctiva of the eye

Food sources: leafy greens, nuts, beans, citrus fruit, asparagus, fortified cereal

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Cleveland Clinic. Vitamin D Deficiency. Available at:–vitamin-d-deficiency. Accessed January 29, 2022.
Modarski B. Pocket Guide Nutrition Focused Physical Exam Third Edition. Academy of Nutrition and Dietetics;2021.
Mayo Clinic. Vitamin C. Available at: Accessed January 30, 2022.
Mayo Clinic. Vitamin B12. Available at: Accessed January 30, 2022.
National Institutes of Health Office of Dietary Supplements. Vitamin B6: Fact Sheet for Professionals. Available at: Accessed February 1, 2022.
National Institutes of Health Office of Dietary Supplements. Folate: Fact Sheet for Professionals. Available at: Accessed February 2, 2022.
Mayo Clinic. Folate (folic acid). Available at: Accessed February 2, 2022.
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About Stacey Phillips

Stacey Phillips, MS, RD is a clinical dietitian working with general medicine, oncology, CKD, renal transplant recipients and living kidney donor patients. Outside of her work, Stacey is passionate about improving the resources available to individuals with chronic kidney disease and actively participates on several renal dietitian committees.

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