Vitamin C is water-soluble. Unlike vitamin D or vitamin A, which your body can store in fat tissue and draw on later, any vitamin C you don't use today gets excreted and is gone by tomorrow [1]. That means there's no such thing as "topping up" for the week. Your levels reset daily, and your intake needs to as well.
This matters more than it sounds. Vitamin C is a cofactor in collagen production, plays a direct role in immune cell function, and works as an antioxidant that helps protect cells from everyday oxidative stress [1]. All of that relies on a consistent daily supply, not an occasional one.
Are you getting enough through food?
Most people assume a healthy diet automatically covers their vitamin C needs. It's a reasonable assumption, but it doesn't fully hold up against the data. A widely cited 2004 study out of the University of Texas compared USDA nutrient data for 43 garden crops between 1950 and 1999, and found statistically reliable declines across six nutrients, including ascorbic acid (vitamin C), alongside protein, calcium, phosphorus, iron and riboflavin [2]. The likely cause isn't the soil alone, it's decades of breeding crops for yield, size, growth speed and pest resistance rather than nutrient density [2]. Bigger, faster-growing produce isn't necessarily more nutritious produce.
Even if a piece of fruit or veg starts out with a healthy amount of vitamin C, a lot of it doesn't survive the trip to your plate. Vitamin C is one of the most heat- and oxygen-sensitive nutrients there is. Research on food processing shows that thermal processing alone, boiling, steaming, roasting, can destroy 50 to 80 percent of a food's vitamin C content [3]. Further losses happen through storage, cutting, and reheating on top of that. It's not that fruit and vegetables are a bad source of vitamin C. It's that between soil quality, harvest, transport, storage and cooking, a lot of what they start with never makes it into your body.
Outright vitamin C deficiency (scurvy) is rare in Australia today, but low-grade inadequacy is more common than most people assume. A 2024 scoping review noted that official dietary assessments likely underestimate the true rate of inadequacy in the Australian population, and called for better screening and updated reference values [6]. Early signs of low vitamin C status include fatigue, low mood, and slower wound healing, symptoms easy to write off as "just being tired" rather than connecting back to diet [6].
Where supplements come in
This is where the research on supplements is genuinely reassuring. A Cochrane review, one of the most rigorous forms of medical evidence available, looked at trials of regular vitamin C supplementation and found it reduced the duration of common colds by around 8 percent in adults and 13.6 percent in children [5]. The effect was even larger, roughly halving cold risk, in people under significant physical stress, such as marathon runners, skiers and soldiers training in sub-arctic conditions [5]. Regular, consistent intake was what produced the benefit, not occasional high doses taken after symptoms had already started [5]. That's the core case for a daily supplement: it's not about replacing food, it's about closing the gap between what your body needs every day and what an average diet reliably delivers.
Recommended daily dose
In Australia, the NHMRC's Recommended Dietary Intake (RDI) for vitamin C is 45mg a day for adults, the amount needed to prevent deficiency-related conditions like scurvy [4]. That's a baseline, not necessarily an optimal target, and it assumes you're actually hitting it through food consistently, which the research above suggests isn't a safe assumption for a lot of people [2][3]. Because vitamin C is water-soluble, your body simply excretes what it doesn't use, rather than storing a surplus [1].
References
1 - National Institutes of Health, Office of Dietary Supplements. Vitamin C Fact Sheet for Health Professionals. ods.od.nih.gov
2 - Davis DR, Epp MD, Riordan HD. Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999. Journal of the American College of Nutrition, 2004;23(6):669-682.
3 - Agriculture Institute. Nutritional Changes and Food Deterioration. agriculture.institute
4 - National Health and Medical Research Council (NHMRC). Nutrient Reference Values for Australia and New Zealand: Vitamin C. eatforhealth.gov.au
5 - Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews, 2013.
6 - The Community Prevalence of Vitamin C Deficiency and Inadequacy, A Scoping Review. PMC, 2024. pmc.ncbi.nlm.nih.gov
0 comments