Gabriella Rao, RD

Continuing on the vitamin wavelength, this week I’m talking about vitamin B12! Vitamin B12 is a water soluble vitamin, which means that it is not stored in the body and requires continued replenishment. It has many roles in the body and is required in greater amounts in endurance athletes.

Functions of vitamin B12:

• Growth and development of nervous system tissues and blood cells
• Red blood cell maturation
• Nerve signaling 
• Brain function
• Energy metabolism 

The RDA for vitamin B12 is 2.4-2.8 mcg per day for adults. Vitamin B12 is found primarily in animal-based foods, though plant-based foods are often fortified with it. For this reason, it is particularly important for vegetarian and vegan athletes to be very intentional with ensuring that they get enough vitamin B12 in their diet. 

Sources of vitamin B12:

• Fish and shellfish
• Meat
• Poultry
• Eggs
• Liver
• Dairy products
• Fortified grains and cereals
• Nutritional yeast

Symptoms of deficiency:

• Fatigue
• Breathlessness
• Pale skin
• Headaches
• Anemia
• Numbness or tingling in hands and feet

Assessment of vitamin B12:

• Serum vitamin B12 is the most common lab assessment of vitamin B12 status.
  • Values of 200-250 pg/mL indicate deficiency.
• Methylmalonic acid, a vitamin B12 associated metabolite, is the most sensitive marker of vitamin B12 status, though less commonly used.
  • Values of greater than 0.271 micromol/L suggests B12 deficiency. 

Supplementation: recommend working with PCP or RD prior to starting supplementation!

• Vitamin B12 supplements are found in several forms, most often as cyanocobalamin, but can also be found as methylcobalamin, adenosylcobalamin, and hydroxycobalamin. B12 can also be found in B-complex supplements or multivitamins. 
• There is no evidence that one form of B12 supplement is absorbed more than others.
• B12 supplement doses range largely, from 5-1,000 mcg.
  • However, the rate limiting factor in absorption is the binding capacity of intrinsic factor. The absorption rate of very high dose B12 supplements is 1-2%, so there is really no need to take high doses since you will excrete most of what you’re taking in. 
• Ensure the brand of supplements you choose is third-party tested (from a company like NSF, Informed Sport, or ConsumerLabs, etc.), so that you can be confident that the supplement doesn’t contain any contaminates and provides the amount of vitamin D listed on the label
  • Third-party tested brands include: Nordic Naturals, Thorne, NOW foods, Momentous, Garden of Life