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Feeling Tired? The Role of Vitamin D and Vitamin B-12 In Energy

Updated: Jun 22, 2022

Most people consider their hectic lives as the source of their fatigue. With school, work, family, friends, and stress, most people feel tired at the end of the day. But, what if the fatigue is persistent or doesn’t seem to improve with sleep. While many health conditions can cause fatigue and it is important that you see your doctor if you have fatigue that is causing significant impairment to your life, there are two vitamins that might be contributing to this lack of energy – vitamin D and vitamin B-12.

Vitamin D

Known as the sunshine vitamin, vitamin D is synthesized when the sun’s energy turns a chemical in your skin into vitamin D3, which is then activated by the kidneys. While vitamin D is probably best known for its role for bone health, it also helps to regulate the immune system and can affect mood, since people with deficiencies often feel tired or depressed. While there is some debate about what “deficient’ is with vitamin D, most experts agree that levels below 20 ng/ml demonstrate an inadequate amount of vitamin D, but some suggest that 20-30 ng/ml suggests a borderline deficiency. There are several groups that are at a higher risk for vitamin D deficiency and they include:

  • Older adults

  • People who spend more time indoors (due to illness, injury, etc.)

  • People who have just taken a course of antibiotics

  • Pregnant women

  • People in later stages of kidney disease

  • People who might have poor absorption of vitamin D due to a medication (such as phenytoin, Pepcid, steroids, or phenobarbital) or a disease such as irritable bowel syndrome (IBS) or Chron’s disease.

  • People with hyperparathyroidism

These groups may also require a higher dose of vitamin D for supplementation. It is suggested that adults who do not have regular, effective sun exposure year round take 600 to 800 international units (IU) of vitamin D3 daily. Vitamin D3 (rather than D2) is suggested because it is closest to the active form that vitamin D uses in the body and is generally suggested for supplementation.

If you experiencing:

  • Tiredness

  • Bone pain

  • Muscle weakness

  • Muscle aches or cramps

  • Mood changes like depression

You should consult with your doctor to have lab tests done to determine if you are experiencing a vitamin D deficiency.

Vitamin B-12

Another vitamin deficiency that might may be causing you to feel sluggish is vitamin B-12. Vitamin B-12, interestingly enough, is only made by certain bacteria and other microorganisms known as archaea which make up the microbiome of other plants and animals. Vitamin B-12 accumulates in animal tissues, which is why meats and milks of animals like cows are rich sources of this vitamin. This is also why vegetarians and vegans should probably supplement vitamin B-12 as they may not be getting a sufficient supply in their diet.

Vitamin B-12 serves several key functions in the body. It makes myelin, a substance that covers nerves and helps the brain function properly by allowing signals to move easily between nerves. It also helps red blood cells mature as well as process protein, fat, and carbohydrates in the body.

Signs and symptoms a potential vitamin B-12 deficiency include:

  • Feeling tired

  • Tingling fingers or toes

  • Feeling depressed or confused

  • Memory loss

  • Bruising easily

  • Rashes or sensitive skin

  • Loss of appetite

  • Nausea and vomiting

Older adults, vegetarians, vegans, people with certain intestinal disorders, and patients taking:

  • Metformin

  • Acid reflux medications like Pepcid (famotidine) or Nexium (esomeprazole)

  • Antibiotics

  • Colcrys (colchicine)

  • Birth control

May be at risk for a Vitamin B-12 deficiency. If you are experiencing any of the above symptoms or fall into any of the above groups, consult your doctor about a possible nutritional deficiency.

Harbor Town Pharmacy is Here to Help

As an independent pharmacy, we offer a wide range of supplements including Pure Encapsulations and Nature’s Truth vitamins. Since we pride ourselves on personalized care if there is a particular supplement you’re looking for, we can look into ordering it from one of our suppliers just for you. Come to us with any questions or concerns you might have regarding supplements, and we’ll gladly answer them.

If you are unsure if you are deficient in Vitamin B12 or D, you can order a lab test and get your blood drawn at a local patient service center. If you need assistance, don't hesitate to contact us.

Written by Brittany Tipton, PharmD Candidate 2023

Reviewed by Kelsey Newell, PharmD


Watanabe F, Bito T. Vitamin B12 Sources and Microbial Interaction. Experimental Biology and Medicine (Maywood). 2018 Jan.

“Treatment of vitamin B12 and Folate Deficiencies” 2 June 2021.

“Vitamin D deficiency in adults: Definition, clinical manifestations, and treatment”

Pelton, Ross and James LaValle. Nutritional Cost of Drugs, 2nd Edition. Morton Publishing. 2004.

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