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Table of Contents
Genetics of beet urine
Summary
After you eat beets, you might be alarmed to see that your urine is blood-red. Or you might be able to eat a ton of beets and have normal yellow urine. If you've heard that red urine after eating beets is a recessive genetic trait, this is not true! The amount of red pigment in urine after eating beets varies smoothly from none to a lot, and family and twin studies have shown that it's not a simple genetic trait. So don't worry if your family includes two red-urine parents and a yellow-urine child, and if you're a teacher, don't use red urine caused by beets as an example of a genetic trait.
Do beets consistently turn some people's urine red?
Some people make red urine after they eat beets, a harmless phenomenon called beeturia or betaninuria, in which the pigment that makes beets red (betanin) is secreted in the urine. Because this looks like blood in the urine (which can be a symptom of serious conditions), someone who doesn't know it is caused by beets can become alarmed and go see a doctor. Other people have normal-looking yellow urine after they eat beets.
In early studies of beeturia (Allison and McWhirter 1956, Saldanha et al. 1960, Saldanha et al. 1962, Watson et al. 1963), people ate beets and then were classified as beeturic or non-beeturic based on the appearance of their urine. In general, people were classified as beeturic if there was any detectable redness in their urine. Instead of just classifying urine as red or yellow, Forrai et al. (1968, 1982) measured the red color in urine with a photometer set to 530 nm, with the absorbance at the yellow wavelength of 660 nm subtracted to give "beet urine units." They found a broad distribution, but no separation into two categories, in a sample of 244 children (Forrai et al. 1968) and 198 twins (Forrai et al. 1982). Pearcy et al. (1991) conducted a similar study and came to the same conclusion, but they do not give their data. Watts et al. (1993) also found a distribution that was skewed but not bimodal. So people cannot be divided into two discrete kinds, those whose urine turns red and those whose urine doesn't turn red; instead, people show continuous variation in how much red pigment they secrete after eating beets.
Several factors affect the amount of betanin secreted after people eat beets, so many people will have visibly red urine after eating some beet dishes but not others. Pearcy et al. (1991) found that the variety of beets, brand, and preparation method all influenced the amount of red color, as did the pH of the urine (betanin is a pH indicator, becoming colorless at basic pH). They also retested several people five times over a period of a few months and found lots of variation from one time to another. Eastwood and Nyhlin (1995) gave people whose urine didn't turn red after eating beets a mixture of betanin and oxalic acid, and they made red urine. Their interpretation was that the oxalic acid prevented betanin from being broken down in the stomach and colon, so that the variation among individuals in the redness of beet urine resulted from varying amounts of oxalic acid in the digestive system. They also found that vinegar-pickled beets caused more people to be beeturic than boiled beets, consistent with the role of acid in causing beeturia.
Watts et al. (1993) fed their subjects beet juice, rather than solid beets, and reported much less variation in betanin secretion than other studies; they suspect that the thoroughness of chewing might be another cause of variation.
Watson et al. (1963) and Tunnessen et al. (1969) found that beeturia was more common in people with iron deficiency, but Forrai et al. (1971) did not find a relationship between betanin and blood iron levels.
Other foods, such as rhubarb and berries, and certain prescription drugs can also cause red urine. And betanin from beets is sometimes used as a red food dye in a variety of foods. So even if you haven't been eating beets, red urine may be just an amusing side effect of what you've eaten, not a symptom of a serious medical condition. Of course, red urine could also mean you have blood in your urine, so if it remains red after a day or so, or you have other symptoms, see your doctor.
Oh, and beets can turn your feces red, too. Mmmm, beets!
Family studies
Allison and McWhirter (1956) visually divided people into beeturic (B) and non-beeturic (N) and looked at a number of families, with the following results:
| Parents | N offspring | B offspring |
|---|---|---|
| N×N | 14 | 2 |
| N×B | 2 | 2 |
| B×B | 0 | 6 |
Because all six offspring of B×B matings were beeturic, they concluded that beeturia was caused by a recessive allele.
Saldanha et al. (1962) looked at a larger number of families, also visually dividing them up into two categories:
| Parents | N offspring | B offspring |
|---|---|---|
| N×N | 18 | 4 |
| N×B | 15 | 19 |
| B×B | 17 | 38 |
The 17 non-beeturic offspring of B×B matings do not fit the idea that beeturia is caused by a recessive allele. Saldanha et al. (1962) considered people with "very weak" amounts of red pigment in their urine as beeturic, while Allison and McWhirter (1956) only counted people who were "distinctly positive" for beeturia.
Twin studies
Forrai et al. (1982) fed pairs of twins uniform amounts of beet juice and measured the red pigment in their urine, rather than just classifying them as beeturic or non-beeturic. They found that monozygotic ("identical") twins were just as different from each other as dizygotic twins. If genes determined the amount of red pigment, monozygotic twins should make the same amount of red pigment as each other, so this makes it clear that beeturia is not strongly affected by genetics.
Further research
Because the large, careful twin study of Forrai et al. (1982) shows that there is no strong genetic influence on beeturia, no one needs to do any more genetics research on it. I can't think of anything else to do with beeturia that would be interesting, but if you can, you should probably give your subjects beet juice (as in Watts et al. 1993) with the pH carefully controlled, and measure the betanin photometrically (as in Forrai et al. 1968, 1982).
References
Allison, A. C., and K. G. McWhirter. 1956. Two unifactorial characters for which man is polymorphic. Nature 178: 748-749.
Eastwood, M. A., and H. Nyhlin. 1995. Beeturia and colonic oxalic acid. Quarterly Journal of Medicine 88: 711-717.
Forrai, G., D. Vágújfalvi, and P. Bölcskey. 1968. Betaninuria in childhood. Acta Paediatrica Academiae Scientiarum Hungaricae 9: 43-51.
Forrai, G., D. Vágújfalvi, J. Lutter, E. Benedek, and E. Soós. 1971. No simple association between betanin excretion and iron deficiency. Folia Haematologica 95: 245-248.
Forrai, G., G. Bankovi, and D. Vágújfalvi. 1982. Betaninuria: a genetic trait? Acta Physiologica Academiae Scientiarum Hungaricae 59: 265-282.
Geldmacher-von Mallinckrodt, M., M. T. Aiello, and M. V. Aiello. 1967. Quantitative erfassung und klinische bedeutung der betaninurie. Zeitschrift für Klinische Chemie und Klinische Biochemie 5: 264-270.
Pearcy, R. M., S. C. Mitchell, and R. L. Smith. 1991. Beetroot and red urine. Biochemical Society Transactions 20: 225.
Saldanha, P. H., L. E. Magalhães, and W. A. Horta. 1960. Race differences in the ability to excrete beetroot pigment (betanin). Nature 187: 806.
Saldanha, P. H., O. Frota-Pessoa, and L. I. S. Peixoto. 1962. On the genetics of betanin excretion. Journal of Heredity 53: 296-298.
Tunnessen, W. W., C. Smith, and F. A. Oski. 1969. Beeturia. American Journal of Diseases of Children 117: 424-426.
Watson, W. C., R. G. Luke, and J. A. Inall. 1963. Beeturia: its incidence and a clue to its mechanism. British Medical Journal 2: 971-973.
Watts, A. R., M. S. Lennard, S. L. Mason, G. T. Tucker, and H. F. 1993. Beeturia and the biological fate of beetroot pigments. Pharmacogenetics 3: 302-311.
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This page was last revised October 26, 2026. ©2026 by John H. McDonald. Content is available under the Creative Commons Attribution-Noncommercial license.