Products with phytosterols are generally well-tolerated, but some supplements may cause nausea, upset stomach, constipation, appetite changes and flatulence, explains pharmacist Jennifer Moll for About.com. Side effects reported in certain studies are associated with higher doses, and they generally fade away with continued use.
Little research exists to support the safety of long-term use of phytosterols as of 2015, so individuals should consult with a doctor before taking the supplement for an extended period, recommends Moll. Also known as plant sterol and stanol esters, phytosterols are capable of reducing blood cholesterol levels by imitating the body's cholesterol in structure, effectively blocking cholesterol absorption, states Cleveland Clinic. Individuals who consume the recommended intake of 2 grams per day may lower LDL cholesterol levels by 14 percent and overall cholesterol levels by as much as 10 percent.
Phytosterols are not retained in the body's tissues and do not inhibit the absorption of vitamins A, D, E or K, according to Cleveland Clinic. Although little research has been done to determine the safety of phytosterols in children as of 2015, intermittent use is generally considered safe by the Food and Drug Administration. The acceptable daily intake is 130 milligrams per kilogram of body weight.