Elevation of serum cholesterol at high altitude and its relationship to hematocrit.

The positive relationship between hematocrit and serum cholesterol may be due to dilution. Accordingly, high hematocrits would yield reduced serum pools for dilution of cholesterol, thus producing higher levels. To test this effect, the relationships between hematocrit and cholesterol were evaluated at low-altitude and high-altitude clinics. Retrospective chart reviews were conducted at Madison, WI (264 m) and Leadville, CO (3105 m) to identify family practice patients who underwent hematocrit and serum cholesterol determinations on the same day. We excluded patients with medical conditions or on medications that affect cholesterol, patients with high glucose and triglyceride levels, and patients with extreme cholesterol levels. Remaining patients (153 in each altitude group) were matched by age and sex. The mean hematocrits and cholesterol levels were compared using analysis of variance. The linear relationships between hematocrit and cholesterol were compared using analysis of covariance. The mean hematocrit was significantly higher at high altitude (47.5% versus 41.3%; p < 0.0005) as were the mean serum cholesterol (190 mg/dL versus 177 mg/dL; p < 0.002) and the low-density lipoprotein:high-density lipoprotein ratio (2.80 versus 2.27; p < 0.05). Whereas a significant, positive relationship existed between hematocrit and cholesterol at low altitude (2.15 mg/dL per %; p < 0.002), no such relationship was found at high altitude. Hematocrit and serum cholesterol were elevated for family practice patients living at high altitudes. Differences exist between altitudes in the relationship between hematocrit and cholesterol. Acclimatization to high altitude and its resultant erythropoiesis may increase serum cholesterol levels. Consequently, relocation to a high altitude may increase the risk of arteriosclerotic cardiovascular disease.