Riboflavin B2 R5P Capsules

Each capsule provides 47.5 mg of riboflavin as riboflavin 5-phosphate, which is 3393% of the nutrient reference value. Take 1 capsule per day with food, as the label directs; the pot holds 60 capsules. The capsule contains riboflavin 5-phosphate with cellulose as the carrier in a vegetarian cellulose shell, and it is vegan and free from gluten, dairy and nuts.

Sources: NIH Office of Dietary Supplements; product label.

R5P is the short name for riboflavin 5-phosphate: vitamin B2 with a phosphate group attached. It is one of the two coenzyme forms the body builds from the vitamin. Chemists know it as flavin mononucleotide, or FMN; the other coenzyme is flavin adenine dinucleotide, FAD, which the body makes from FMN. Riboflavin itself is the plain form of the vitamin, a yellow compound that is destroyed by light. Vitamin B2 dissolves in water, so the body stores very little and needs a supply every day. These capsules contain R5P only, not plain riboflavin.

Sources: NIH Office of Dietary Supplements; Food Standards Scotland.

R5P capsules and plain riboflavin end up in the same place. The body absorbs the vitamin as free riboflavin and then attaches the phosphate itself, and NIH reports that the bioavailability of free riboflavin is similar to that of the FMN and FAD forms. Taking the phosphate form therefore does not skip a step, and the choice between them is about form rather than absorption. What limits how much of any form is kept is the amount: about 95% of vitamin B2 is absorbed up to a ceiling of roughly 27 mg in one dose, and little is absorbed above that.

Sources: NIH Office of Dietary Supplements.

R5P supplies vitamin B2, whose two coenzymes sit at the centre of energy production: they let cells release energy from carbohydrate, fat and protein. The vitamin also activates two other vitamins, since converting vitamin B6 to its active form needs FMN and making niacin from tryptophan needs FAD, and it helps the body absorb iron from food. It helps keep homocysteine in the normal range and keeps skin, eyes, the nervous system and the lining of the mouth healthy. Research on doses far above the daily need centres on migraine: in one trial of 55 adults, 400 mg a day reduced attacks by two a month against placebo, while two small trials in children found no effect.

Sources: NIH Office of Dietary Supplements; Food Standards Scotland.

A 47.5 mg capsule sits above the 40 mg a day that Food Standards Scotland advises as a ceiling from supplements. It is also above the roughly 27 mg the body can absorb from one dose, so part of each capsule passes straight through. No harm has been reported from vitamin B2 at amounts up to 400 mg a day for three months or more, which is why the United States set no upper limit, but NIH adds that the absence of reports does not prove very high intakes are harmless. UK adults need about 1.3 mg a day for men and 1.1 mg for women. One capsule a day is the label amount; anything beyond it is a practitioner's call rather than a self-directed one.

Sources: Food Standards Scotland; NIH Office of Dietary Supplements.

R5P capsules give a fixed 47.5 mg a day in one step. By contrast the R5P liquid gives 1.6 mg per ten-drop serving, just over the daily reference value. A capsule suits anyone who wants an active B2 supplement at the higher fixed amount, for instance alongside methylfolate and B12 in a methylation routine. Anyone who only wants a maintenance level is better served by the liquid.

Sources: NIH Office of Dietary Supplements; product label.

Yes: riboflavin turns urine bright yellow within hours of taking it. That is harmless and is simply the vitamin the body did not need leaving. At 47.5 mg a capsule, almost everyone taking these will notice it.

Sources: NIH Office of Dietary Supplements.

R5P is most often taken with the other B vitamins, and it works closely with them. It is needed to activate vitamin B6 and to make niacin. NIH lists no known interactions between vitamin B2 and prescription drugs, and no adverse effects from food or supplements beyond yellow urine. Some drugs and long courses of light treatment can lower the body's vitamin B2, but that is a reason to check status, not to avoid the supplement. Anyone pregnant or breastfeeding, or taking prescribed tablets, should speak to a GP or pharmacist first.

Sources: NIH Office of Dietary Supplements; Food Standards Scotland.