Vitamin C Ascorbic Acid

Vitamin C is one of the easiest supplements to choose well, because the real questions are dose, form and how it sits in your stomach. These are the questions our naturopaths ask in store.

A good fit if

• Fresh fruit and vegetables are genuinely hard to fit into your week and you want a dependable baseline
• You eat little or no meat, or take a plant-based iron supplement, and want vitamin C alongside it
• Plain ascorbic acid upsets your stomach and you want to know what a buffered form actually changes
• You want to understand what really differs between a plain tablet and a liposomal liquid before you choose
• You'd rather split a modest amount across the day than swallow one large tablet at breakfast

Check with us first if

• You've had kidney stones or have been diagnosed with hyperoxaluria. The strongest evidence linking high-dose vitamin C to stones is in people who already have hyperoxaluria.
• You have kidney disease or reduced kidney function, since your kidneys clear vitamin C.
• You take iron supplements, or you're being monitored for high iron. Vitamin C increases how much iron you absorb, which helps in one situation and not in the other.
• You're having chemotherapy or radiotherapy. The NIH advises checking with your oncologist before taking antioxidant supplements, especially at high doses.
• You take niacin together with simvastatin, where vitamin C may dull the expected rise in HDL ('good') cholesterol.
• You get cramps, loose bowels or nausea at your current dose. That's unabsorbed vitamin C drawing water into your gut, and the dose or form needs changing.

• Ascorbic acid. Best known for: The reference form and the cheapest per gram; its acidity is what sensitive stomachs react to. Absorption: The benchmark every other form is measured against; unmetabolised surplus is simply passed in urine. Typical use: Powder or tablet, more usefully split across the day than taken as one large dose.
• Sodium ascorbate. Best known for: Buffered and non-acidic; the usual pick for reflux-prone people and for high-dose powders. Absorption: Bioavailability equivalent to ascorbic acid; the sodium it carries is the thing to check if you watch salt. Typical use: Powders stirred into water, and common in practitioner high-dose formulas.
• Calcium ascorbate, including Ester-C. Best known for: Buffered with calcium and marketed as longer-lasting; Ester-C also supplies vitamin C metabolites. Absorption: A direct comparison found no difference in plasma vitamin C or urinary excretion between ascorbic acid, Ester-C and ascorbic acid with bioflavonoids. Typical use: Tablets and capsules for people who find plain ascorbic acid harsh; contributes calcium to the daily total.
• Other mineral ascorbates (magnesium, potassium, zinc). Best known for: Non-acidic blends that deliver a mineral alongside the vitamin C. Absorption: Absorbed as ascorbate like the other salts; in practice the mineral, not the vitamin C, sets the ceiling. Typical use: Powders and combination tablets. Zinc ascorbate is capped at 50 mg of zinc per day in Australian medicines.
• Liposomal vitamin C. Best known for: Phospholipid encapsulation, sold on the promise of higher plasma levels at a premium price. Absorption: Evidence of a meaningful advantage over plain ascorbic acid at everyday doses is limited rather than settled. Typical use: Oral liquids and sachets; comfortably the most expensive option per gram.
• Wholefood vitamin C (acerola, camu camu, rose hip, Kakadu plum). Best known for: Naturally occurring vitamin C alongside the plant's own compounds, including bioflavonoids. Absorption: No bioavailability advantage over synthetic ascorbic acid has been demonstrated; synthetic and natural forms test the same. Typical use: Berry powders supplying a few hundred milligrams a serve, usually sold as foods rather than listed medicines.

Reference values. The NHMRC Recommended Dietary Intake is 45 mg a day for adult men and women, rising to 60 mg in pregnancy and 85 mg while breastfeeding at ages 19 to 50. The adult average requirement (EAR) is 30 mg a day. The Australian reference values say 'This EAR provides enough vitamin C for smokers', even though the same document notes that blood vitamin C is 40% lower in male smokers. That differs from some overseas guidance, which adds extra for smokers.

Typical supplemental range. Australian tablets usually contain 500 to 1,000 mg each, and powders are commonly dosed at 1 to 3 g. That's ten to sixty times the RDI, which is why, for most people, the practical limit is what your bowels can handle rather than what your body needs.

Upper level. No Upper Level has been set. The NHMRC says, word for word: 'It is not possible to establish a UL for vitamin C, but 1,000 mg/day is a prudent limit.'

Worth knowing. Your cells are full at intakes of around 100 mg. Above roughly 200 mg, blood levels rise only a little and the rest leaves in your urine. So splitting your dose keeps more in circulation than taking one large one. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Red capsicum, raw: 95 mg per half cup: more than double the adult RDI
• Orange juice: 93 mg per three-quarter cup
• Orange, whole: 70 mg per medium fruit
• Kiwifruit: 64 mg per medium fruit
• Broccoli, cooked: 51 mg per half cup
• Kakadu plum (gubinge), Australian native: reported as the highest ascorbic acid level of any fruit in the world, though measured values vary widely between trees and seasons

This list is the part of the page we will not shorten. If any of it applies to you, talk to one of our naturopaths or your doctor before starting.

• Haemochromatosis or iron overload. High doses could exacerbate iron overload and result in tissue damage (NIH).
• Diagnosed hyperoxaluria. The strongest kidney-stone evidence relates to this group; avoid gram-level doses.
• History of kidney stones, or kidney disease and reduced renal function. Discuss before high doses.
• Iron supplementation or iron monitoring. Vitamin C increases non-haem iron absorption.
• Chemotherapy or radiotherapy. NIH advises discussing antioxidant supplements with the treating oncologist.
• Niacin taken with simvastatin. Vitamin C may attenuate the HDL increase.
• Diarrhoea, nausea and abdominal cramps. The most common complaints at high doses, caused by unabsorbed vitamin C in the gut.
• Zinc-containing ascorbate products. Australian medicines are capped at 50 mg of zinc per day and must carry a zinc warning above 25 mg.
• Ascorbyl palmitate products. Australian oral medicines are capped at 100 mg of ascorbyl palmitate per day.
• Doses above 1,000 mg/day. NHMRC has set no Upper Level but names 1,000 mg/day as a prudent limit.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before starting.