Quick answer

NIH's fact sheets give no best time of day to take vitamin C. The daily amount matters more than the hour: moderate doses are absorbed well, while single doses of 500 mg or more are absorbed less completely. Taking it with a meal that contains plant iron helps you absorb that iron.^1,2,3

Key facts

A single 200 mg dose was fully absorbed in a controlled NIH study.²
White blood cells are saturated at about 100 mg of vitamin C a day.²
Vitamin C taken at the same time as levothyroxine might raise how much of the medicine is absorbed.⁴
Most multivitamins already contain vitamin C, so check the label before adding a separate one.⁵

Morning or night?

NIH's vitamin C fact sheets give no advice on the time of day to take it.^1,5

The body keeps blood levels of vitamin C in a narrow range. Once cells are full, at about 100 mg a day, extra is passed in urine, which makes the daily total, rather than the hour on the clock, the number to watch.^1,2

So choose a time you will remember, morning or evening, and keep to it.

1,000 mg tablets and other large doses

About 70% to 90% of vitamin C is absorbed at intakes of 30 to 180 mg a day. Above 1 g a day, less than half is absorbed, and the absorbed excess is passed in urine.¹

In the NIH study, single doses of 500 mg or more were not absorbed in full, and more of them ended up in urine. A 1,000 mg tablet is therefore far more than cells can hold, and part of it is not absorbed.²

Large single doses are also where stomach upset comes from. Vitamin C that is not absorbed stays in the gut and draws water in. The research used here does not test splitting a large dose through the day.¹

With meals that contain iron

Eating foods that contain vitamin C at the same meal as plant sources of iron helps the body absorb more of that iron.^1,3

This is the main timing effect in the sources. The vitamin C and the plant iron need to be in the same meal, for example peppers with beans or orange juice with an iron-fortified cereal.³

Timing around medicines and tests

Ask your pharmacist or doctor first

Vitamin C taken at the same time as levothyroxine might increase how much of the medicine is absorbed.⁴

Reported in studies

Ask your pharmacist or doctor first

Prescribing labels for extended-release mixed amphetamine salts name ascorbic acid, which is vitamin C, as an example of an acidifying agent that lowers blood levels of amphetamine and can make it less effective. Tell your prescriber if you take vitamin C.^6,7

On the medicine's label

If you take either medicine, ask your pharmacist when to take vitamin C. Bring the label of any multivitamin too, since most contain it.⁵

High intakes might cause falsely high or low readings on some blood glucose meters.⁴

Questions people ask

Should I take vitamin C in the morning or at night?

NIH gives no advice either way. The amount you take each day matters more than the hour, so pick a time you will keep to.¹

Should I split a 1,000 mg dose?

The sources here do not test splitting. They do show that single doses of 500 mg or more are absorbed less completely than smaller ones, and that cells are full at about 100 mg a day.²

Can I take vitamin C with my other supplements?

Check what they already contain. Most multivitamins have vitamin C, so add up the vitamin C from every product and keep the total under the 2,000 mg adult upper limit.⁵

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line Immune Support Men's Multi

Sources

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