Review: radiation can alter the immune system

Cells of the body under a microscope Source: adventtr/Stock/GettyImagesPlus

A new scientific review shows that even radiation doses in the range of 20–100 milligrays can have an effect on the immune system. The threshold is therefore below the values used in radiotherapy, for example. The review took the form of an evaluation of over 200 studies by an international team of researchers, in which the Federal Office for Radiation Protection (BfS) was also involved. Particular attention was paid to analysing the effects of different levels of radiation doses.

High radiation doses of over one gray, such as those that can be used in radiotherapy, are known to have a significant impact on the immune system and can lead to adverse long-term health outcomes. However, even doses of 20–100 milligrays are apparently sufficient to trigger minor but permanent immunological changes. These values can result from occupational radiation exposure over a period of many years, for example. According to current information, these doses have no direct impact on health. Further investigation is needed to determine whether they can result in adverse long-term health outcomes.

Ionising radiation can be produced artificially or can form naturally as a result of the radioactive decay of certain atomic nuclei. In addition to natural radiation, humans can be exposed to radiation from medical and technical applications, for example. Certain occupational groups, such as flight crew or medical personnel, are also exposed to radiation.

The lower the dose, the greater the need for research

The researchers' evaluation of the studies reveals that the effects vary depending on the radiation dose:

• A single whole-body dose of less than 100 milligrays may affect the performance of the immune system and accelerate its ageing. However, persistent changes to the immune system were also observed at lower exposure levels. Nevertheless, according to current information, these biological changes do not have a direct impact on health.

• In the case of doses of less than 20 milligrays, it is not possible to draw firm conclusions for either acute or repeated exposure.

• In contrast to these observations, doses of between 100 milligrays and 1 gray can have an anti-inflammatory and pain-relieving effect when administered locally. However, this only applies when chronic inflammation have already occurred. These doses are therefore used for the localised treatment of joint inflammation, for example.

Unlike for lower doses, the relationship between higher radiation doses and the immune system has been well researched. This research only observed adverse effects, such as pro-inflammatory processes or temporary suppression of the immune system. These findings are largely based on results relating to radiotherapy patients and the studies of Japanese survivors of the atomic bombs at Hiroshima and Nagasaki.

Different scenarios as a basis for the current evaluation

Personal dosimeter for monitoring individuals who are occupationally exposed to radiation.

The current evaluation also incorporated studies relating to different exposure scenarios. These included studies that examined single but large radiation doses as well as studies on sections of the population that are exposed to increased levels of natural radiation or contamination, including in the workplace. In addition to acute exposure, the evaluation also took account of chronic exposure to radiation. Experimental studies and clinical observations confirm that the immune system is affected by lower radiation doses that have accumulated over a longer period of time.

To allow better classification of doses, typical dose values are compiled on the BfS website. For example, an effective dose of 100 millisieverts corresponds to single whole-body irradiation with 100 milligrays of gamma radiation.

Outstanding questions relating to chronic radiation exposure

In their summary, the scientists reaffirm the need for research projects on the underlying mechanisms and their possible long-term effects, especially in relation to lower-level radiation exposure. This would help to clarify whether radiation-induced immunological changes encourage the development of cardiovascular diseases or cancer.

The review entitled "Low dose ionizing radiation effects on the immune system" was published in the journal Environment International. The editorial, whose lead author is from the BfS, provides readers with an introduction to the subject matter.