Study raises questions about food products meant to block cholesterol absorption

Plant sterols, which are naturally found in many foods but are also added to some foods intended to inhibit cholesterol absorption, are present in artery plaques, according to a new study (PDF) in the June 7, 2005, issue of the Journal of the American College of Cardiology.

“This study shows that plant sterols, which occur in our food, are absorbed to a small degree. They are found in blood serum and enter into plaques in arteries in the same proportion as cholesterol in the blood serum. It is totally unknown whether they have anything to do with development of arterial plaques or whether the health risks are coupled with cholesterol only,” said Tatu A. Miettinen, M.D., Ph.D., at the University of Helsinki in Finland.

Certain foods with high levels of plant sterols are considered to be “heart healthy” because they partially block absorption of cholesterol, thereby reducing levels of LDL “bad” cholesterol. Some brands of margarines and juices that are supplemented with plant sterols are marketed as beneficial to heart health because of their ability to reduce cholesterol levels. However, it is not known whether absorbing high levels of plant sterols in place of cholesterol has any effect on health.

This study is the first of its kind in living patients that directly measured levels of plant sterols and cholesterol in blood serum and artery plaques. The researchers studied 25 consecutive patients who were undergoing carotid endarterectomy procedures to remove plaques clogging the carotid arteries.

“The major new observation of the present study was that the higher the ratio of the dietary absorption sterol (cholestanol, campesterol, sitosterol and avenasterol) to serum cholesterol, the higher the ratio was also in the carotid artery wall,” the authors wrote.

Ira Tabas, M.D., Ph.D., at Columbia University, who was not connected with this study, called it fascinating research that raises questions about the possibility of direct atherogenic effects of plant sterols, but he said that these results should not alarm people.

“There are many components in plants that are highly beneficial, so you don’t want to give the message that people shouldn’t eat plants,” Dr. Tabas said.

He pointed out that if the results had been different and researchers had not found plant sterols in the artery plaque of patients with high blood serum levels, then the idea that they could have a role in promoting plaques would have seemed unlikely. However, the results of this study leave the door open to the possibility that plant sterols somehow affect one or more processes related to plaque development and other aspects of atherosclerosis.

“Until we are able to determine one way or the other whether these plant sterols are directly atherogenetic and whether or not these products could be doing harm in some people, we don’t want to set off any waves of panic. It’s purely speculative at this point. But it certainly raises the question, and so it deserves further exploration,” Dr. Tabas said.

Richard V. Milani, M.D., F.A.C.C., at the Ochsner Heart and Vascular Institute in New Orleans, who also was not connected with this study, said it is important to keep the findings in perspective. He said while the results are important to researchers, the meaning for people who eat plant sterols to lower LDL cholesterol is not yet known.

“We can’t draw any conclusions from this. This isn’t an article meant to give the public an answer. This is just bringing up more questions. It’s a good paper, but again, it’s hypothesis-generating. We don’t know that having a higher level of plant sterols in the blood or in the plaque is necessarily bad. There’s no simple take-home message for the public here,” Dr. Milani said.

The American College of Cardiology, a 31,000-member nonprofit professional medical society and teaching institution, is dedicated to fostering optimal cardiovascular care and disease prevention through professional education, promotion of research, leadership in the development of standards and guidelines, and the formulation of health care policy.