B Complex and Vitamin C: Best Time to Take

Quick answer

Both are water-soluble, and no NIH source describes a B complex and vitamin C interfering with each other. A reported drop in B12 from high-dose vitamin C has not been confirmed. Adults need 75 to 90 mg of vitamin C a day, and single doses of 500 mg or more are absorbed less completely.^1,2,3

Key facts

All eight B vitamins and vitamin C dissolve in water, and the body passes what it does not use in urine.^1,4,5
Adults need 90 mg of vitamin C a day for men and 75 mg for women, with an upper limit of 2,000 mg from food and supplements combined.²
In a controlled study a single 200 mg dose of vitamin C was fully absorbed, while single doses of 500 mg or more were absorbed less completely.³
NIH says reports that high vitamin C intakes lower vitamin B12 have not been confirmed, and some came from errors in lab tests.¹
Levothyroxine appears in the cautions for both: vitamin C might raise its absorption, and biotin in a B complex can distort thyroid tests.^6,7

What the two have in common

Vitamin C and the B vitamins share one property that shapes everything about taking them: they dissolve in water. The body keeps only modest stores, absorbs a share that falls as the amount rises, and passes the rest in urine. That is why neither group tends to build up the way a fat-soluble vitamin can.^1,4

Within that shared property the details differ. Vitamin C is absorbed at 70% to 90% at intakes of 30 to 180 mg a day, and less than half above 1 g. Riboflavin is absorbed only up to about 27 mg from a single dose. Vitamin B6 is absorbed well but quickly passed. B12 is absorbed at about 2% of a 500 mcg dose. For thiamin, a smaller share is absorbed above about 5 mg a day.^1,4,5,8,9

Our sources do not describe vitamin C competing with any B vitamin for absorption, and we found no trial that tested a B complex with and without vitamin C.^1,8

What each is graded for

Provides vitamin B12, which the nervous system needs to develop and work normally*^8,10

Moderate evidence

A long-established role rather than a finding from supplement trials. NIH describes vitamin B12 as required for the development, myelination and function of the central nervous system, and running short can cause numbness and tingling in the hands and feet. In trials of older adults, vitamin B12 taken alone or with other B vitamins did not change scores on thinking and memory tests.

Amount studied: Recommended amount for adults: 2.4 mcg of vitamin B12 a day

Contributes to the protection of cells from oxidative stress*^1,2,11,12

Moderate evidence

A well-established nutrient function. NIH describes vitamin C as an antioxidant that limits damage from free radicals and helps regenerate vitamin E, and EU regulators permit this wording for foods that are at least a source of vitamin C. It describes a normal function, not a measured health outcome: in healthy young women given 30 to 2,500 mg a day, blood and urine markers of the body's own oxidative damage did not change at any dose.

Amount studied: Recommended intake: 75 mg a day for women and 90 mg for men, from food and supplements

Best time to take a B complex with vitamin C

NIH's vitamin C sheets give no advice on the time of day, and the B vitamin sheets give none either. What the sources do back up is thinking about the size of each dose, because absorption falls at the top end for several of these vitamins.^1,2,8

The question arises mainly when a separate vitamin C supplement is added to a B complex. Then dose size is the thing to watch: single doses of 500 mg or more were absorbed less completely than 200 mg, so splitting a large amount across the day gets more of it absorbed. The sources give the B complex itself no clock time.^3,8

A separate point matters if you also take iron or eat plant sources of iron: NIH says vitamin C at the same meal raises how much of it is absorbed, which has nothing to do with the B vitamins.¹³

Amounts and our products

Vitamin C and the B vitamins that most often reach a limit^2,14,15,16
	Recommended, adults	Upper limit, adults
Vitamin C	75 mg (women), 90 mg (men)	2,000 mg from food and supplements
Niacin	14 mg NE (women), 16 mg NE (men)	35 mg from supplements and fortified foods
Vitamin B6	1.3 mg at ages 19 to 50	100 mg from all sources
Folate	400 mcg DFE	1,000 mcg of folic acid
Other B vitamins	Varies	None set for thiamin, riboflavin, B12, pantothenic acid or biotin

What’s in ours

Men's Multi: Vitamin C, 150 mg per serving, from the label
Immune Support: Vitamin C, 180 mg per serving, from the label

What’s in ours

Men's Multi: Vitamin B1, 7 mg per serving, from the label

Checking a claim, and who should ask first

A claim that circulates online is that vitamin C destroys vitamin B12 when the two are taken together. NIH addresses it directly, as the entry below shows. The honest summary is that the idea is unconfirmed, and some of the reports behind it came from laboratory errors, not from changes in people.¹

Reports that high intakes lower vitamin B12 and copper, wear tooth enamel or cause allergic reactions have not been confirmed, and some came from errors in lab tests.¹

Ask your pharmacist or doctor first

Vitamin C taken at the same time as levothyroxine might increase how much of the medicine is absorbed.⁶

Reported in studies

Ask first if you have hemochromatosis or another cause of iron overload, since NIH says people with this condition should avoid vitamin C supplements.¹
Ask first if you have had kidney stones or have kidney disease.¹
Ask first if you take levothyroxine, a statin or an amphetamine medicine, each of which vitamin C is documented to affect.^6,17
Tell your doctor and the lab if you take biotin in a B complex before blood tests, because it can make some results read falsely high or low.^18,19
Ask first if you use a blood glucose meter, since high vitamin C intakes can cause false readings on some meters.⁶

Questions people ask

Can you take B complex with vitamin C?

Our sources describe no effect of one on the other, and the two are routinely sold together in multivitamins. Watch the total against the niacin and B6 limits, and ask a pharmacist if you take levothyroxine or the other medicines named above.^1,8,14

Does vitamin C destroy vitamin B12?

NIH says reports that high vitamin C intakes lower vitamin B12 have not been confirmed, and that some came from errors in lab tests. Separately, B12 is a nutrient that people over 50 and people who eat no animal foods may need to watch for other reasons.^1,20

What is the best time to take a B complex and vitamin C?

Our sources name no time of day for either. If you take 500 mg or more of vitamin C, splitting it across the day gets more of it absorbed than one dose.^2,3

Which is more likely to cause an upset stomach?

High doses of vitamin C can cause diarrhea, nausea and stomach cramps because the unabsorbed part draws water into the gut. In a B complex, the usual complaint is flushing from niacin as nicotinic acid, and bright yellow urine from riboflavin.^1,4,21

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.