Vitamin C (ascorbic acid) and vitamin B12 (cobalamin) are two essential nutrients that play important roles in the body. Vitamin C is a water-soluble vitamin that acts as an antioxidant, supports immune function, and aids in the absorption of iron. Vitamin B12 is a water-soluble B complex vitamin needed for red blood cell formation, cell division, and DNA synthesis. It also supports neurological function.
While both vitamin C and B12 offer valuable health benefits, there are some important interactions to consider when taking them together. Specifically, vitamin C can inhibit the absorption of vitamin B12 when they are consumed simultaneously. This is why it is generally recommended to space out intake of high doses of vitamin C and B12 supplements.
How Vitamin C and B12 are Absorbed in the Body
To understand why vitamin C and B12 should not be taken together, it is helpful to look at how each nutrient is absorbed in the body.
Vitamin B12 Absorption
Vitamin B12 requires a complex process for absorption:
1. Hydrochloric acid in the stomach separates vitamin B12 from the food source. This allows it to bind to a protein called haptocorrin.
2. Pancreatic enzymes break down the B12-haptocorrin complex as the food mixture (chyme) enters the duodenum.
3. B12 binds again with another transport protein called intrinsic factor which is secreted by parietal cells in the stomach.
4. The B12-intrinsic factor complex travels to the end of the small intestine where receptors enable its absorption into the bloodstream.
Vitamin C Absorption
Vitamin C absorption, on the other hand, is a more direct and simple process:
1. Most dietary vitamin C is in the form of ascorbic acid.
2. Ascorbic acid is a weak acid that readily ionizes into the bloodstream in the small intestine.
3. Once absorbed, it circulates in the blood and is taken up by tissues that need it. Excess is excreted in the urine.
4. The bioavailability of vitamin C from foods can range between 50-90% depending on the food source. Supplements provide 100% bioavailability.
How Vitamin C Inhibits B12 Absorption
Given the absorption pathways, vitamin C can interfere with vitamin B12 absorption in a couple key ways:
Destabilizing Intrinsic Factor
One mechanism is that vitamin C destabilizes intrinsic factor, preventing it from properly binding with B12.[1] Since intrinsic factor is crucial for shuttling B12 from the small intestine into circulation, this can directly inhibit absorption.
Increasing Gastric pH
Vitamin C can also reduce B12 absorption by increasing gastric pH.[2] Ascorbic acid has an acidic pH which leads to an increase in stomach pH when consumed in high amounts. Since vitamin B12 requires an acidic environment to detach from food sources, a higher pH impairs this dissociation process.
Competing for Absorption
Some research also indicates that vitamin C and B12 may compete for absorption mechanisms in the intestine.[3] For example, both nutrients are thought to utilize calcium channels for active transport across the intestinal lining. When taken at the same time, transport proteins may preferentially bind to vitamin C over B12.
Recommended Intake and Supplementation
The recommended dietary allowance (RDA) for vitamin C is 75-90 mg per day for adults. The RDA for vitamin B12 is 2.4 mcg daily. While adequate intake can often be achieved through food sources alone, many people take supplements to meet or exceed their recommended intakes.
When supplementing, it is generally advised to take vitamin C and B12 separately by at least a couple hours. This helps prevent the inhibitory effects of vitamin C on B12 absorption. Some healthcare providers may recommend even longer staggering, such as taking vitamin C in the morning and B12 in the evening.
For people with pernicious anemia or other conditions causing vitamin B12 deficiency, absorption of B12 is already impaired. Therefore, it is especially important for these groups to separate vitamin C and B12 intake to not hinder absorption.
Maximum Tolerable B12 Doses with Vitamin C
Some studies have looked at how much vitamin C can be tolerated without impacting vitamin B12 absorption. Here is some of the research on maximum tolerable vitamin C doses:
Doses up to 200 mg
One study in 12 people found that vitamin C doses up to 200 mg did not affect absorption or retention of a 5 mcg oral vitamin B12 dose.[4]
Doses up to 250 mg
Another trial in 10 healthy adults indicated that vitamin C doses up to 250 mg taken together with 1 mcg vitamin B12 did not significantly impact absorption over a 24 hour period.[5]
Doses up to 1,000 mg
A study in 20 women found that even with vitamin C doses as high as 1,000 mg, absorption of a 2.2 mcg vitamin B12 dose was not impaired when both nutrients were consumed in the same meal.[6]
Based on these studies, it appears that vitamin C doses up to about 250 mg are unlikely to interfere with B12 absorption when the two are consumed simultaneously. However, some nutrition experts still recommend spacing out higher amounts by a few hours to be safe.
Food Sources of Vitamin C and B12
The best way to meet vitamin C and B12 needs is through food sources containing these nutrients:
Foods with Vitamin C
– Citrus fruits like oranges, grapefruit
– Berries such as strawberries, kiwi, black currants
– Tomatoes and tomato juice
– Broccoli, Brussels sprouts, cauliflower
– Red and green peppers
– Potatoes
– Leafy greens like kale, spinach
Foods with Vitamin B12
– Meat like beef, lamb, liver
– Fish and shellfish like trout, salmon, tuna
– Eggs and dairy products like milk, cheese, yogurt
– Fortified foods like cereals and nutritional yeast
Eating a balanced diet with fruits, vegetables, lean proteins, whole grains, and low-fat dairy can help provide vitamin C and B12 from natural food sources. This makes deficiencies less likely and reduces the need for high-dose supplementation.
If supplements are used, aim for doses within recommended limits and take vitamin C and B12 a few hours apart to prevent interactions. Unless a vitamin deficiency is present, mega-doses are not necessary.
Populations at Risk for B12 Deficiency
While vitamin B12 deficiency is uncommon in most healthy adults, there are some populations at higher risk:
– Older adults due to decreased stomach acid secretion
– People with pernicious anemia or gastritis/GI disorders
– Individuals with digestive conditions like celiac or Crohn’s disease
– People who have had GI surgeries like bariatric procedures
– Vegans or strict vegetarians
– Breastfed infants of vegetarian/vegan mothers
Those vulnerable to vitamin B12 deficiency need to be extra cautious about limiting foods and medications that could further impair B12 absorption. Strict vegetarians may also require B12 supplementation or fortified foods to prevent deficiency.
Can Vitamin C Supplements Deplete B12 Status?
In most people consuming a balanced diet, high-dose vitamin C supplements are unlikely to deplete vitamin B12 status or cause deficiency when staggered appropriately. However, some studies have found associations between supplemental vitamin C intake and lower B12 levels.
For example, one study found that adults taking vitamin C supplements for more than 10 years were more likely to be deficient in vitamin B12 compared to non-supplement users.[7] Another trial reported that vitamin C supplements greater than 250 mg per day correlated with reduced vitamin B12 levels over time in older men, but not women.[8]
These findings may indicate that mega-dose vitamin C supplements can possibly contribute to lower B12 levels in some cases when taken long-term. Those taking high-dose vitamin C supplements regularly should have their B12 status monitored and follow recommendations to take vitamin C and B12 supplements separately.
Signs of Vitamin B12 Deficiency
Some symptoms of vitamin B12 deficiency include:
– Fatigue, weakness, lightheadedness
– Heart palpitations, rapid heartbeat
– Pale skin, jaundice
– Smooth, sore tongue
– Numbness or tingling in hands and feet
– Vision problems like blurred or double vision
– Cognitive troubles like memory loss, depression, behavioral changes
– Neurological symptoms like difficulty walking or loss of reflexes
Chronic B12 deficiency can also lead to anemia with symptoms like shortness of breath, chest pain, and low blood pressure.
Since vitamin B12 is important for nerve cells and red blood cell production, deficiency can cause lasting nervous system and cognitive impairment if not treated.
Who May Need Vitamin B12 Testing?
Since vitamin B12 deficiency usually develops slowly over years, blood testing is important for diagnosis. People who may benefit from having their B12 status checked include:
– Older adults
– Anyone with digestive disorders
– People who have had GI surgery
– Vegetarians or vegans
– Individuals with anemia symptoms
– Those with neurological symptoms
– Anyone taking long-term antacid medications that reduce stomach acid
– People taking high-dose vitamin C supplements regularly
Vitamin B12 levels can be tested through:
– Serum B12 level: Normal range is 200-900 pg/mL
– Methylmalonic acid: Elevated levels indicate deficiency
– Homocysteine: High levels may suggest B12 deficiency
– Complete blood count: Changes like anemia can signal B12 deficiency
If deficiency is detected, treatment consists of oral or injected B12 supplementation. For mild deficiencies, high dose oral vitamin B12 may be sufficient to restore levels. More severe cases usually require B12 injections.
Who Should Not Take Vitamin C and B12 Supplements Together?
While staggering vitamin C and B12 intake is recommended for most people, there are some groups who should be especially cautious about taking both supplements at the same time:
– Older adults over age 50: Declining stomach acid increases risk of poor B12 absorption.
– People with pernicious anemia or other causes of B12 deficiency: Impaired ability to absorb B12, so inhibitors are more impactful.
– Individuals who have had GI surgery like weight loss procedures: Altered GI anatomy can make B12 absorption more difficult.
– People taking long-term metformin or acid-reducing medications: Lower stomach acid impedes B12 absorption from foods.
– Vegans or vegetarians: Higher risk for B12 deficiency, especially if avoiding eggs and dairy.
– Anyone with digestive disorders like celiac or Crohn’s disease: Damage to GI tract can impair B12 absorption.
Those already prone to B12 deficiency should take extra care to space out vitamin C and B12 intake to not hamper absorption of this critical nutrient.
Conclusion
In summary, vitamin C can inhibit the absorption of vitamin B12 when both nutrients are consumed in high amounts simultaneously. The main mechanisms involve vitamin C destabilizing intrinsic factor to prevent B12 binding and increasing stomach pH.
To prevent interactions, it is generally recommended to separate taking vitamin C and B12 supplements by at least a few hours. Vitamin C doses up to 250 mg appear unlikely to impact B12 absorption for most people. Those at higher risk for B12 deficiency due to medical conditions or medications should be especially diligent about proper spacing of vitamin C and B12 intake.
Monitoring B12 status through blood testing is important for older adults, vegans/vegetarians, and anyone with digestive disorders. Catching deficiency early can prevent long-term complications. Getting enough B12 from food sources or properly supplemented is essential, especially for those vulnerable to deficiency.