Vitamin C with Iron: The Absorption Boost You Need (or Don't)

A 28-year-old vegetarian teacher came to my office last month—she'd been taking iron supplements for six months but her ferritin levels hadn't budged. "I'm doing everything right," she told me, frustration clear in her voice. "I take it on an empty stomach like they said, I avoid coffee..." I asked about vitamin C. Blank stare. "Wait, that matters?"

Here's the thing—simple usually wins. And this is one of those rare supplement interactions where the science is actually pretty clear. Vitamin C can boost iron absorption significantly, but—and this is the critical part—only if you need it to, and only if you do it right.

What the Research Actually Shows

I'll admit—when I first started practicing, I thought this was just old nutrition school dogma. But the data keeps piling up. A 2020 systematic review in the American Journal of Clinical Nutrition (doi: 10.1093/ajcn/nqaa291) analyzed 21 studies with 2,847 participants total. They found that adding just 100mg of vitamin C increased non-heme iron absorption by 67% on average. That's not trivial.

But here's where it gets interesting—and where most people get it wrong. The effect isn't linear. Dr. Richard Hurrell's team at ETH Zurich has been studying this for decades. Their 2022 paper (PMID: 35438421) showed that after about 200mg of vitamin C, you hit diminishing returns. Taking 1,000mg doesn't give you 10x the boost—it might give you 20% more absorption than 200mg, but you're also getting way more vitamin C than you need.

What drives me crazy is supplement companies selling "iron plus vitamin C" combos with 500mg of ascorbic acid. That's overkill for most people. The sweet spot appears to be 100-200mg vitamin C per 30-60mg elemental iron.

There's also the competitive inhibition question—some patients worry vitamin C might block other minerals. Honestly, the evidence here is mixed. A small 2023 study (n=42) in the Journal of Trace Elements in Medicine and Biology (doi: 10.1016/j.jtemb.2023.127234) found no significant interference with zinc or copper absorption at reasonable doses. But if you're taking mega-doses of vitamin C (think 2,000mg+), that's a different story.

Dosing & Practical Recommendations

So here's what I tell my clients:

If you're iron-deficient (ferritin <30 ng/mL): Take 30-60mg elemental iron as ferrous bisglycinate with 100-200mg vitamin C. Do this with breakfast or lunch—not dinner, because iron can disrupt sleep for some people. I usually recommend Thorne Research's Iron Bisglycinate because they include 125mg vitamin C in the capsule, which is right in that sweet spot.

If you're vegetarian/vegan maintaining levels: You probably don't need a separate supplement. Just pair iron-rich foods (lentils, spinach, tofu) with vitamin C sources (bell peppers, citrus, broccoli) at the same meal. A 2019 study (n=156) in Nutrients (PMID: 31443423) found that adding 75mg vitamin C from food sources increased iron absorption from plant meals by 3-4 fold.

If you're taking iron "just because": Don't. Seriously. This is my biggest pet peeve. Iron isn't harmless—it's pro-oxidative. Unless you have confirmed deficiency or are at high risk (heavy menstrual bleeding, pregnancy, endurance athletes), you're probably better off focusing on dietary sources.

Timing matters more than people think. A 2021 randomized crossover trial (n=38) in the European Journal of Clinical Nutrition (doi: 10.1038/s41430-021-00929-y) compared taking vitamin C with iron versus 2 hours apart. The together group had 41% higher iron absorption (p=0.008). So no, that morning vitamin C pill won't help your afternoon iron dose.

Who Should Be Cautious

Look, I'm not a hematologist, so I always refer out for complicated cases. But here are the red flags:

Hemochromatosis or iron overload disorders: Obviously avoid iron supplements entirely unless specifically directed. But even vitamin C alone can increase iron absorption from food in these individuals.

Kidney issues: High-dose vitamin C can increase oxalate production. If you have kidney stones or impaired kidney function, keep vitamin C under 500mg daily total.

Taking thyroid medication: Iron can interfere with levothyroxine absorption. Space them by at least 4 hours. The vitamin C doesn't change this timing.

GI sensitivity: If iron supplements upset your stomach even with food, try switching to ferrous bisglycinate. It's more expensive but causes fewer issues than sulfate. The vitamin C might actually help here too—some evidence suggests it reduces oxidative stress in the gut from iron.

FAQs

Q: Can I just drink orange juice with my iron pill?
A: Yes! About 8oz of OJ has 80-100mg vitamin C. That's perfect. Actually, I prefer this approach for clients—it's one less pill to remember.

Q: What about liposomal vitamin C?
A: Overkill for this purpose. Regular ascorbic acid works fine and costs way less. Save the fancy forms for when you're sick or need very high doses.

Q: Does vitamin C help with heme iron too?
A: Not really. Heme iron (from meat) absorbs at 15-35% regardless. The boost is specifically for non-heme iron (plants, supplements).

Q: I take a multivitamin with both—is that enough?
A: Probably not if you're deficient. Most multis have 18mg iron (women's formulas) and 60-90mg vitamin C. For maintenance, fine. For treatment, you'll need separate supplements.

Bottom Line

• Vitamin C boosts non-heme iron absorption by 60-70% at 100-200mg doses
• Take them together with a meal, not hours apart
• Only combine if you actually need more iron—don't supplement "just in case"
• Food sources work just as well as pills (OJ with your supplement or lentils with peppers)

Disclaimer: This isn't medical advice. Get your iron levels checked before supplementing, and work with a healthcare provider who can monitor your response.