The truth about vitamin C and mild stomach upset

Vitamin C is a water-soluble vitamin that isn’t stored very well in the body. The Reference Nutrient Intake for vitamin C is set in the UK at 40mg, which is the amount for 97.5% of the population to ward off deficiency disease, rather than being recommended for optimum health. 

An important thing to note is that our need for vitamin C demands change according to lifestyle factors – are we warding off an infection? Are we stressed? Do we smoke or are we exposed to other toxins (1)?

How much is too much?

So, what is deemed a safe limit to avoid side effects? In the UK the FSA Expert Group on Vitamins and Minerals in 2003 stated that “there is insufficient data to set a Safe Upper Level for vitamin C” suggesting that the vitamin is safe at much higher levels than the current RNI.

However, they do go on to say that intakes over 1,000mg might cause abdominal pain and diarrhoea (2). In the US, there is a big difference: the Safe Upper Levels are set at 2g per day, which is the dose at which they say mild stomach upset might occur (3).

Managing sensitive digestion

Higher doses of vitamin C can be a challenge for those with sensitive digestive systems, although many people taking high doses don’t have any issues at all. Research is divided as to what that level is – normally between 2-6g (2, 3).

If stomach upset does occur, then reduce the supplement level and/or make sure you take the supplement with food or liquid. The addition of sodium bicarbonate to act as a buffer to the ascorbic acid (as in Tonic Health’s supplements) can help here too.

Ascorbic acid has long been established as the best bioavailable form of vitamin C in supplements, so for those of us without sensitive digestive systems – or who can find their manageable dose – it's definitely the form of choice (4).