Alternative vitamin C forms and how the body takes them up
What it found
In healthy adults, some alternative vitamin C supplements raised vitamin C levels in immune cells more than plain ascorbic acid, and one form caused fewer stomach complaints.
The authors say more research is needed to confirm effects on immune health.
What they found
Studies in people
Vitamin C in immune cells
Four studies measured vitamin C in leukocytes. Some found higher leukocyte vitamin C with Calcium ascorbate EC than with plain ascorbic acid, including at 24 hours after a 1000 mg dose.
Plasma and serum levels
Seven studies reported plasma vitamin C levels, and some found more favourable levels with alternative forms than with ascorbic acid or placebo. One study found higher serum vitamin C with vitamin C lipid metabolites than with Calcium ascorbate EC, calcium ascorbate, or ascorbic acid.
Stomach complaints
Calcium ascorbate EC caused fewer epigastric adverse events and was rated as better tolerated than ascorbic acid. In one study, 72% of participants rated Calcium ascorbate EC as very good versus 54% for ascorbic acid.
Colds and immune markers
One study found fewer colds and a shorter duration of severe symptoms with Calcium ascorbate EC than with placebo. Another study found improved neutrophil function and higher natural killer cell counts with 500 mg Calcium ascorbate EC compared with ascorbic acid.
Liposomal absorption
Liposomal vitamin C led to higher plasma and leukocyte vitamin C levels than plain ascorbic acid in one study. Another study found liposomal vitamin C was 1.8 times more bioavailable than non-liposomal vitamin C.
Slow-release vitamin C
One study found that slow-release vitamin C raised plasma vitamin C levels above baseline at 12, 16 and 24 hours after a 500 mg dose, and both peak concentration and total exposure were higher than with placebo.
What the authors conclude
“In conclusion, the type and delivery modality of vitamin C can impact its bioavailability and functionality.”
Also in their conclusions
- They conclude that the type and delivery form of vitamin C can affect how well it is absorbed and how it works in the body.
- They say Calcium ascorbate EC showed better tolerability and fewer gut side effects than traditional ascorbic acid, and may increase vitamin C in immune cells.
- They advise that more research is needed to confirm the effects of alternative vitamin C forms on immune health.
How it was done
The authors wanted to pull together the evidence on how well different vitamin C supplement forms are absorbed and retained, and what they do for tolerability, immunity and infection, to see if one form is better than plain ascorbic acid.
They searched medical databases for studies published from 2000 to October 2024 and found 13 randomised controlled trials in healthy adults, mostly young or middle-aged. The studies tested calcium ascorbate with vitamin C metabolites, liposomal vitamin C, slow-release vitamin C, or vitamin C lipid metabolites, at doses of 250, 500 or 1000 mg, given once or over several days.
What it can’t tell you
- The studies used different designs, doses and ways of measuring vitamin C, so the authors could not properly compare the forms or say one is superior.
- No study looked at how much vitamin C is retained in tissues, which is important for immune function.
- Most studies were short, and the authors say longer trials with more diverse people are needed to show effects on immune health.
Who paid
- Conflicts
- P.C.C. acts as an ad hoc adviser to Bayer Consumer Care, Haleon, and dsm-firmenich. R.B.K. has conducted research on nutritional supplements funded by grants and contracts awarded to the universities with which he has been affiliated, including for The Bountiful Co. (Ronkonkoma, NY, USA); received an honorarium for making scientific presentations; and served as a paid scientific expert. He is a co-founder of the International Society of Sports Nutrition and currently serves as Chair of Creatine for Health Scientific Advisory Board for Alzchem (Trostberg, DEU) and as a scientific adviser to Trace Minerals (West Haven, UT, USA) and Oath Nutrition (Trove Brands, Lehi, UT, USA). D.L.M. is a former member of the Nature’s Bounty Co. Scientific Advisory Council.
- Authors work at
- University of Southampton, UK; University Hospital Southampton NHS Foundation Trust and University of Southampton, UK; Texas A&M University, USA
The paper
- Title
- Enhanced Vitamin C Delivery: A Systematic Literature Review Assessing the Efficacy and Safety of Alternative Supplement Forms in Healthy Adults
- Type
- Systematic review
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Calder PC, Kreider RB, McKay DL (2025). Enhanced Vitamin C Delivery: A Systematic Literature Review Assessing the Efficacy and Safety of Alternative Supplement Forms in Healthy Adults. Nutrients. doi:10.3390/nu17020279Free full textPubMed 39861409DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error