Concepts familiar from grade-school algebra have broad ramifications in computer science.
MIT has released details of an internal review on the four published nutrition studies involving iron and calcium which were carried out by the late MIT Professor of Nutrition Robert S. Harris and others.
MIT President Charles M. Vest has expressed his concern over the apparent lack of fully informed consent involved in nutritional research conducted by MIT at the Walter E. Fernald State School in Waltham, MA four decades ago. "I was sorry to hear that at least some of the young people who participated in this research and their parents apparently were unaware that the study involved radioactive tracers," he said Friday. "People should not unknowingly become the subjects of research studies of this type. We have had in place for more than two decades at MIT numerous safeguards and approval processes that assure informed consent of human subjects of any research.
"It is important to recognize that the purpose of these studies was to improve understanding of nutritional processes in order to promote health of young people, and that radiation exposure appears to have been well within even today's limits," Dr. Vest said.
Professor of Physics J. David Litster, vice president and dean for research, reviewed the four articles published in professional journals in the 1950s plus a PhD thesis that dealt with the work. The published studies made no mention of the matter of informed consent, and the review was therefore limited to the scientific aspects and the radiation exposures. According to records reviewed to date, Fernald school authorities informed the parents of the research. It is not clear, however, whether those authorities said that the studies involved the use of low levels of radioactive tracers of iron and calcium.
At the time, the custom was that the patients' medical doctors or clinicians were the ones who communicated with the patients or the subjects of research. In the late 1960s and early 1970s, the federal government assigned to the US research institutions the responsibility for obtaining the consent of research subjects.
The research used minute amounts of radioactive iron and calcium as diagnostic tracers of the digestive process. The exposures to radiation were 30 percent to 99 percent below the much more stringent limits that are in effect today. The occupational and research limits today for people 18 and under is 500 millirems per year, in addition to normal background radiation of 300 millirems per year plus any medical radiation (see Tech Talk Radiation Guide, Jan. 5, 1994).
The adult occupational limit and the research limit are 5,000 millirems per year above background levels, plus any medical radiation. For a fetus, the mother's occupational limit is also 500 millirems, but it is recommended that exposure to the mother (and fetus) be limited to no more than 50 millirems per month. (In the 1950s, the limit for an adult was 15,000 millirems; for a person 18 or under, it was 1,500 millirems.) Levels of exposure to radioactivity, like alcohol intoxication levels, depend on a person's weight.
The dietary iron study by Professor Harris and three other MIT researchers showed that iron supplements are more effective when taken between meals, because eating cereals decreases iron absorption.
To track the iron absorption, less than a billionth of an ounce of a radioactive iron tracer was mixed with breakfast cereal. Seventeen youths, aged 12 to 17, had seven oatmeal or farina breakfasts over a period of 40 weeks. The average exposure in the iron study was 230 millirems, or 54 percent below the current limit. The exposure of the lightest youth was 330 millirems (34 percent below the current limit) and the exposure of the heaviest youth was 170 millirems (66 percent below the current limit).
The calcium studies were pioneering studies which laid the foundation for much subsequent research on osteoporosis. The scientists gave 45 youths and one adult two exposures totaling 4 to 12 millirems (99 percent to 97 percent below the current limit). To interpret these figures, it should be noted that the extra radiation dose for a round trip airplane flight from Boston to California is 12 millirems. Also, 10 millirems is the amount of exposure per year from daily use of salt substitute (potassium chloride).
The research was done by F. Bronner, Professor Harris, C.J. Maletskos, all of MIT, and C.E. Benda, who had an appointment at the Harvard Medical School and was clinical director at the Fernald School.
The first calcium study, published in 1954, involved 19 youths aged 13 to 17 with a low-calcium diet. They received two oatmeal or farina breakfasts three weeks apart, each containing in the milk 0.85 microcuries (two-trillionths of an ounce) of radioactive calcium45 as a tracer.
The second study, published in 1956, involved 17 youths aged 10 to 16 with a moderate-calcium diet; each of them also received two oatmeal or farina breakfasts three weeks apart containing the same amount of radioactive calcium. The two studies showed that if sufficient calcium was present in the diet, phytates (a class of chemical compounds) in food such as oatmeal have no effect on the amount of calcium absorbed by the body. The amount of dietary calcium required was about three times the amount of phytate in the diet; this requirement is met by most American diets (but not, perhaps, by very low-calcium diets in other countries).
A third calcium study, also published in 1956, involved nine youths (aged 11 to 15) who had the same breakfast as those in the other two studies. They also received a direct injection of calcium containing as a tracer slightly less than two-trillionths of an ounce (0.75 microcuries) of radioactive calcium. An adult also received an injection with a proportionally higher dosage.
The purpose of the third study was to establish a baseline for the metabolism of calcium in the blood, including how much is excreted via the urine and feces after the calcium, in a reverse absorption process, passes through the wall of the lower gastrointestinal tract. The third calcium study found that calcium in the body system is excreted mostly through the urine, with only a third being excreted in the feces. It also showed that the body excretes injected calcium very slowly (because the calcium goes to the bones and stays there).
By comparison, radiation exposure from therapeutic treatment for medical conditions is vastly larger. For example, radioactive iodine drinks for hyperthyroidism deliver 10,000,000 millirems to the thyroid gland and 20,000 millirems to the rest of the body.
A person's normal lifetime risk of contracting cancer from all sources--tobacco, chemicals, background radiation, medical radiation etc.)--is one in three. The lifetime risk for a fatal cancer is one in five. For the iron study, there was an increased lifetime risk of a fatal cancer ranging from about one in 2,000 to about one in 4,000. For the calcium study, the increased lifetime risk of a fatal cancer ranges from about one in 55,000 to one in 160,000.
A version of this article appeared in the January 12, 1994 issue of MIT Tech Talk (Volume 38, Number 19).