Where your DNA places you among other people, and the studies behind it.
Not tailored to your result, and not medical advice
Quit or Avoid Smoking: Smokers typically run a higher red cell count than non-smokers, and the raised reading is not by itself a sign of marrow disease. When chronic smokers stopped, their elevated hemoglobin concentration, packed cell volume and red cell count all returned rapidly toward normal within about two weeks. The authors concluded that at least some of these abnormalities are an acute, reversible effect of cigarette smoking rather than a response to tissue damage. Stopping is one of the clearest behavioral influences on this number. Journal of the Royal Society of Medicine (PMC)
Pair Plant Iron With Vitamin C: Iron sits at the center of the hemoglobin molecule, so iron supply limits how many functional red cells the body can build. Haem iron, the form found in meat and fish, is absorbed at roughly 15 to 35 percent, while absorption from plant foods is reported at about 7 to 9 percent for green leafy vegetables, 4 percent for grains and 2 percent for dried legumes. In feeding studies, increasing amounts of ascorbic acid added to a formula meal raised iron absorption from 0.8 to 7.1 percent, whereas polyphenol-rich tea cut absorption from iron-fortified bread by 56 to 72 percent and added calcium cut it by 18 to 27 percent. Eating vitamin C rich foods alongside plant iron sources, and taking tea or coffee between meals rather than with them, works with that chemistry. ACS Omega (PMC)
Get B12 and Folate From Food: Red cell production depends on vitamin B12 and folate for DNA synthesis, and without them the marrow produces underdeveloped red cells that are larger than normal and do not work properly. A diet that includes meat, fish and dairy usually provides enough B12, so people who avoid those foods depend on fortified products instead. Good sources of folate include broccoli, Brussels sprouts, asparagus, peas, chickpeas and brown rice. Diet is not the only cause: in the UK the commonest reason for B12 deficiency is pernicious anemia, an autoimmune condition affecting the stomach that blocks absorption, which is why an unexplained result is worth discussing with a clinician rather than treating as a food problem. NHS
Take Loud Snoring Seriously: Repeated dips in blood oxygen during sleep drive erythropoietin release and push red cell production upward. Among 605 young adults with untreated obstructive sleep apnoea, red blood cell count, hemoglobin and haematocrit all rose with apnoea severity, 8 percent met the hemoglobin criterion for polycythaemia, and mean overnight oxygen saturation rather than the apnoea count itself was the independent predictor. Men with severe sleep apnoea had close to three times the odds of raised hemoglobin compared with milder disease, an association the authors reported was rare in women. Habitual loud snoring, witnessed breathing pauses or heavy daytime sleepiness are worth raising with a clinician. Nature and Science of Sleep (PMC)
Account For Training and Fluid Shifts: A red cell count is a concentration, so anything that changes plasma volume changes the number without changing how many red cells you actually have. Endurance training expands plasma volume within a few days of intensive work, lowering measured red cell count, hemoglobin and haematocrit even though total hemoglobin mass is normal or increased, a pattern often called sports anemia. A low reading in an athlete is not always dilution, though: iron deficiency is reported in up to 52 percent of female adolescent athletes and in 30 to 50 percent of endurance athletes. This is the honest limit of lifestyle here, since diet and training shift this number only modestly in people who are not deficient, and a persistent unexplained high or low result is a conversation with a clinician rather than something to manage on your own. Life (PMC)
How much of this is genetic?
Genetics explains 40% of why people differ in this trait. The rest is environment, daily habits and chance.
Heritability estimate: Evans et al. 1999, Twin Research; blood cell GWAS (Astle et al. 2016, Cell)
Background and further reading
The red blood cell (RBC) count is one of the core numbers reported on a complete blood count (CBC). It reflects how many red cells are circulating per microliter of blood, typically around 4.5 to 5.9 million in men and 4.1 to 5.1 million in women. Red cells are packed with hemoglobin and are responsible for carrying oxygen from the lungs to the tissues and returning carbon dioxide, so RBC count tracks closely with hemoglobin and hematocrit. It sits in the middle of a normal biological range for most people; values are naturally higher in men than in women, largely because testosterone stimulates red cell production. A count meaningfully below the reference range contributes to a diagnosis of anemia, while a persistently elevated count (polycythemia or erythrocytosis) can occur with chronic low oxygen, dehydration, or certain bone-marrow conditions.
Genetic Basis: Red blood cell production, or erythropoiesis, is a highly heritable quantitative trait shaped by hundreds of common genetic variants of small effect. Large genome-wide association studies of blood cell traits, including work by van der Harst and colleagues and later the Astle and Vuckovic studies of UK Biobank participants, have mapped hundreds of loci influencing RBC count and related indices. Well-characterized genes include those governing the erythropoietin signaling and iron-handling pathways, such as TMPRSS6 (iron regulation via hepcidin), SH2B3/LNK (a negative regulator of cytokine signaling in blood-cell precursors), and the HBS1L-MYB region on chromosome 6, which is a major regulator of erythroid output. A polygenic score aggregates the small contributions of many such variants into a single genetic tendency.
Other Factors: RBC count is strongly influenced by environment and physiology, not genetics alone. Living at high altitude raises red cell production over weeks as the body adapts to thinner air, and chronic smoking nudges counts upward through mild oxygen deprivation. Endurance training, by contrast, often lowers the measured count because blood plasma volume expands more than red cell mass, a harmless adaptation sometimes called dilutional or sports pseudoanemia. Iron, vitamin B12, and folate availability are essential for making red cells, so nutritional deficiency lowers counts, as can blood loss, pregnancy (through dilution), chronic kidney disease (via reduced erythropoietin), and inflammation. Hydration status matters too: dehydration concentrates the blood and can transiently raise the measured count. Because of these influences, a single reading is a snapshot, and this genetic score describes an average lifelong tendency rather than any one lab result.
The published research behind your score, and the variants it draws on.
20 published scores from 9 studies
The RBC count score combines 20 polygenic scores drawn from 9 published studies.
Vuckovic D, et al. The Polygenic and Monogenic Basis of Blood Traits and Diseases. Cell (2020)
These traits are influenced by some of the same genes and variants as this one
Hemoglobin: The oxygen-carrying protein in red blood cells, measured on a routine blood count.
HbA1c: Glycated hemoglobin, reflecting average blood sugar levels over the past 2-3 months.
Platelet Count: The number of platelets, the clotting cell fragments, per volume of blood.
Content updated August 2026.
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