Immunity and radiation

How ionizing radiation affects the body

When we talk about radiation exposure and its effects on the body, we usually mean ionizing radiation (IR) – the kind that can damage living tissue. The fact is, we are exposed to ionizing radiation every day either from natural sources (coming from radon, minerals, rocks, soil, and cosmic rays) or from man-made sources (from exposure to X rays, CT scans, radiotherapy, nuclear accidents and workplace radiation).

So, what is ionizing radiation? And how can it damage your cells and tissues? IR is electromagnetic radiation that contains enough energy to rip apart electrons from atoms and molecules of the cells. This leads to the production of highly volatile free radicals and their by-products that disrupt the chemical structure of cells and structures that lie within; such as DNA, mitochondria, proteins and lipids. This change in the chemical composition affects their ability to function normally.

What does a cell go through when it is exposed to ionizing radiation?

  1. The cell suffers no damage when radiation passes through it.
  2. The cell repairs itself after a brief exposure and can survive and replicate without any error.
  3. Exposure to low doses over longer periods may damage cellular DNA, causing genetic mutations that can be passed to future generations.
  4. DNA damage can also cause the cell to become cancerous.
  5. High doses of radiation over a short span can cause cells to die.

How radiation damages your DNA

IR can damage DNA through two main mechanisms:

  • Direct damage: when radiation collides with DNA molecule and breaks it.
  • Indirect damage: when water molecules in the body absorb the radiation and become ionized, forming a destructive trail of free radicals and their metabolites. The majority of the DNA damage occurs due to this free radical mechanism. Damage to DNA is of particular consequence as DNA carries all the genetic information your cells need to function, grow and produce new cells. If there is damage to DNA, the instructions that control all these functions and reproduction also become corrupted – leading to mutations.

Can you repair DNA damage caused by ionizing radiation?

IR can damage DNA in two ways: by causing a single strand break or double strand break. Your body has specialized repair mechanisms to deal with single strand DNA damage and restore cellular functions. But major problem occurs when the body tries to repair the double strand break. It is a complicated process and may lead to errors when broken ends are joined back, leading to either cell death or DNA mutations (changes in the DNA sequence that alter normal cellular functioning). Mutations, for example, affect the cell’s ability to divide in a normal fashion. Uncontrollable cell division can give rise to cancerous growth in the body.

Acute versus chronic radiation exposure

When the body is exposed to extremely high doses of radiation, even for a short period of time, it can cause radiation sickness, and even death within days or weeks.

A single large exposure to radiation can cause overwhelming damage to internal organs by killing large numbers of cells. Nausea and vomiting are the earliest symptoms of radiation sickness. In fact, the time span between exposure and the first signs of vomiting is used to estimate the dose absorbed by a person. Radiation sickness can also cause bleeding (loss of platelets), fatigue and fainting (loss of red blood cells), increased risk of infections (loss of white blood cells) and bloody diarrhea. In case of severe exposure, symptoms can show up within minutes. Most of these effects, also called deterministic or non-stochastic, are due to damage to the bone marrow, gastrointestinal tract, and central nervous system.

Chronic, low dose radiation exposure

Ionizing radiation is known to increase the risk of cancer and other non-cancer diseases long after one is initially exposed. These risks include birth defects, infertility, cataracts and heart disease. But what about low dose exposure?

Most experts in this field agree that there is no dose so low that it will not have any harmful effects on the body. This is called ‘stochastic effect’, meaning there is no threshold dose. As explained by Dr. Ian Fairlie, a London-based independent consultant on radioactivity: “Stochastic means an all-or-nothing response: you either get cancer or you don’t. As you decrease the dose, the effects become less likely and your chance of cancer declines all the way down to zero dose. The corollary is that tiny doses, even well below background, still carry a small chance of cancer: there is never a safe dose, except zero dose.” [1]

While the science looks divided on whether low dose, chronic exposure exerts any significant health issue, the latest research is providing evidence that even low dose can be harmful in the long-term. A 2017 study found that a dose as tiny as 0.5 Gy (something you would receive after repeated CT scans) can increase your risk of cardiovascular disease long after you have been exposed. [2]

Internal radiation exposure

After a nuclear fallout (1986 Chernobyl accident and 2011 Japan’s Fukushima nuclear disaster), organisms can get irradiated both externally and internally. Internal exposure happens when you ingest, absorb or inhale radioactive material present in your immediate environment (through contaminated air, food and water).

Radioactive isotopes have a sly mechanism of making their way into the body: by mimicking nutrients. When these isotopes enter the body, they target and lodge in all kinds of tissues and organs – such as thyroid, bone, lungs, endocrine glands, heart, liver and kidneys. This kind of internal exposure is believed to be many times more harmful than external exposure. These isotopes keep emitting radioactive energy as they decay, causing persistent damage to living cells and tissues, leading to cancer and a host of non-cancer diseases.

For example, Cs 137 mimics potassium, a mineral that you need for a healthy heart beat and normal muscle contractions, among other important functions. When you are exposed to Cs 137, most of it is accumulated into the muscles, interfering with heart functions and causing irregular heart beat (cardiac arrhythmias), heart attack and high blood pressure. Similarly, Strontium-90 mimics calcium and is deposited in your skeletal system, thus affecting bone health by irradiating bones, bone marrow and the surrounding soft tissue.

Then there is “By stander effect”

The radioactive energy not only affects irradiated cells but has the potential to damage the neighbouring, out of field cells too. This phenomenon of cell damage is called the bystander effect. When a cell is irradiated, it has a rippling effect on the surrounding cells – stimulating similar kinds of unwanted outcomes in those cells too, although with slightly different mechanisms than DNA damage (for example, through intracellular signalling and increased oxidative stress). This leads to an increased risk of mutations, genomic instability and cell death. [3] [4]

However, it must be noted that these bystander responses are also believed to enhance the repair mechanism, reduce radiation damage and even get rid of severely damaged cells. [5]

Not all cells are affected in the same way

The effect of radiation on the human body depends on a lot of factors – the type of radiation, dose, whether you have been exposed from the outside or inside, frequency and severity of exposure (one time or repeated low dose exposure over a long period), organs irradiated, age and even gender. Large doses of radiation can result in biological effects that may occur within days or weeks while others like cancer may not show up for years.

It is also believed that a small, single dose may not be enough to cause significant damage. But what is noteworthy is that each additional exposure (from combined sources including background radiation, medical procedures and nuclear accidents) builds up in the body and adds up over a lifetime, increasing the risk of cancer and other conditions.

The cells most affected by ionizing radiations (nuclear radiations and from medical scans) are those that multiply rapidly (DNA is most exposed when a cell is multiplying). For this reason, fetal tissue, bone marrow stem cells (which gives rise to different types of blood cells – red blood cells, white blood cells and platelets), and cells in gastrointestinal tract are especially sensitive to radiation damage. This is also the reason why radiotherapy works to kill rapidly dividing cancer cells.

Now a very important question is: Can nutrition help prevent, or repair damage caused by radiation? Well, a good diet with lots of vitamins, minerals and anti-oxidants plays a critical role in combating and even reversing the toxic outcomes of radiation on the body. Stay tuned for our next blog to read more on the role of nutrition in preventing as well as fighting radiation damage.

References:

  1. Ian Fairlie. Fukushima: Thousands Have Already Died, Thousands More Will Die. Counter Punch. 2015.
  2. Azimzadeh et al. Proteome analysis of irradiated endothelial cells reveals persistent alteration in protein degradation and the RhoGDI and NO signalling pathways. Internation Journal of Radiation Biology. 2017
  3. Toledo et al. Genomic instability induced in distant progeny of bystander cells depends on the connexins expressed in the irradiated cells. Int J Radiat Biol. 2017
  4. A Marin et al. Bystander effects and radiotherapy. Rep Pract Oncol Radiother. 2015
  5. Klammer at al. Bystander effects as manifestation of intercellular communication of DNA damage and of the cellular oxidative status. Cancer Lett. 2015