Combining supplements: what works together and what to avoid

Combining supplements is an increasingly important topic in modern sport and healthy living. Taking several supplements at the same time is common, but few people know that nutrients can significantly affect each other’s absorption. An evidence-based approach to combining supplements helps you get the maximum benefit without wasting resources.

How does combining supplements affect nutrient absorption?

The body absorbs nutrients in the small intestine through several different transport and diffusion mechanisms. Some minerals use the same transporters – in that case competition arises, and a large amount of one nutrient inhibits the absorption of another. Other compounds, however, promote each other’s absorption: acidic compounds improve the solubility of minerals, and fat-soluble vitamins are absorbed better together with dietary fats.

Timing your supplement intake is closely linked to combining supplements: even compatible combinations can deliver a smaller result if they are taken at the wrong time of day.

Which supplements enhance each other’s effect?

Vitamin D and calcium. Vitamin D regulates the calcium transport protein TRPV6 in the gut, so calcium absorption increases markedly when vitamin D levels are adequate. A randomized controlled trial showed that calcium together with vitamin D reduced the risk of osteoporotic fractures in older women to a statistically significant degree (Jackson et al., 2006).

Vitamin D and magnesium. To become active, vitamin D needs hydroxylase enzymes in the liver and kidneys, and magnesium is a cofactor for these enzymes. Uwitonze and Razzaque (2018) found that insufficient magnesium intake inhibits the conversion of vitamin D into the active hormone calcitriol.

Vitamin C and plant-based iron. Ascorbic acid converts trivalent iron into divalent iron, which is absorbed more efficiently via the DMT1 transporter. Siegenberg et al. (1991) showed that vitamin C prevents the inhibitory effect of polyphenols and phytic acid on the absorption of plant-based iron.

Omega-3 fatty acids and dietary fats. Fish oil capsules are recommended to be taken with a fat-rich meal: Dyerberg et al. (2010) demonstrated that the bioavailability of omega-3 fatty acids rises significantly when they are consumed together with dietary fats.

You can read more about building logical combinations in the article Special combinations.

Which supplements shouldn’t be taken together?

Calcium and iron. Calcium inhibits the absorption of both heme and non-heme iron by competing for the same transporters. Hallberg et al. (1991) showed that 300 mg of calcium reduced iron absorption by up to 40%. It is therefore advisable to separate calcium and iron supplements by at least two hours.

Creatine and caffeine. Vandenberghe et al. (1996) found that caffeine neutralized the ergogenic effect of creatine loading: phosphocreatine stored in the muscle did not deliver the expected strength results when participants took caffeine at the same time. Practical advice: take creatine in the morning and a caffeine-based pre-workout at a different time.

Zinc and iron in high doses. Both compete for the DMT1 transporter. The NIH Office of Dietary Supplements recommends avoiding more than 25 mg of zinc together with an iron supplement, as this may inhibit iron absorption and, with longer use, impair copper metabolism (NIH ODS – Zinc).

If you want to know which supplements have passed quality control in Estonia, also take a look at Tasting dietary supplements at TÜ ASK – it gives an overview of how well the actual composition matches the label.

How does alcohol affect the action of supplements?

Alcohol doesn’t go well with supplement use. Ethanol interferes with the absorption of B vitamins – especially B1, B6 and folic acid – and impairs liver function, which is key to activating many vitamins. In addition, alcohol’s diuretic effect increases the excretion of magnesium and zinc through the kidneys, reducing the effectiveness of these supplements. You can find more detailed information on how alcohol relates to physical training load in the article How alcohol fits with training.

Practical recommendations for combining supplements through the day

The following schedule gathers the evidence-based recommendations into a simple daily routine:

• In the morning with a meal containing fat: vitamin D + K2, omega-3, magnesium.
• At midday: calcium (separate from iron), vitamin C together with plant-based iron.
• Before training: caffeine-based pre-workout (creatine at a different time).
• After training: whey protein + creatine monophosphate.

Combining supplements doesn’t require complicated protocols – knowing a few basic rules is enough to make your daily routine significantly more effective.

References

• Hallberg L, Brune M, Erlandsson M, Sandberg AS, Rossander-Hulthén L. (1991). Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. Am J Clin Nutr. 53(1):112–9. PMID: 1986835.
• Siegenberg D, Baynes RD, Bothwell TH, et al. (1991). Ascorbic acid prevents the dose-dependent inhibitory effects of polyphenols and phytates on nonheme-iron absorption. Am J Clin Nutr. 53(2):537–41. PMID: 1846468.
• Vandenberghe K, Gillis N, Van Leemputte M, Van Hecke P, Vanstapel F, Hespel P. (1996). Caffeine counteracts the ergogenic action of muscle creatine loading. J Appl Physiol. 80(2):452–7. PMID: 8899067.
• Jackson RD, LaCroix AZ, Gass M, et al. (2006). Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 354(7):669–83. PMID: 16481635.
• Uwitonze AM, Razzaque MS. (2018). Role of magnesium in vitamin D activation and function. J Am Osteopath Assoc. 118(3):181–189. PMID: 29480918.
• Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB. (2010). Bioavailability of marine n-3 fatty acid formulations. Prostaglandins Leukot Essent Fatty Acids. 83(3):137–41. PMID: 20638827.

You’ll find plenty of supplements here: https://turg.fitness.ee/et

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