Can light impact our Biology-Part 2
Everyday, everywhere stories from the lens of science
This week’s article will build upon what we learned in our last post, which reviewed the basics of electromagnetic radiation and detailed the impact of visible spectrum on human physiology. I highly recommend reading that post if you have not already.
A natural question that comes next is: Can light invisible to our eye also impact us and if yes, How ?
We will uncover the answers to this question in this article.
If you recall from the earlier post, our eyes can only perceive light in range of 400-700nm. That means light spectrum below 400nm and above 700nm is invisible to our eyes. This invisible spectrum can be broadly classified as: 1) Short-wavelength light spectrum: gamma radiation, x-rays and ultra-violet (UV) rays and 2) Long wavelength spectrum: radio waves, microwaves and infra-red radiation. Although your eyes cannot see light in these spectrum, they can have potential and long lasting effects on your biology.
This article will focus on the 3 different rays of short wavelength spectrum, one by one we will understand both the harmful and useful effects of this spectrum.
In the follow-up article we will explore the impact of long wavelength spectrum on our Biology.
Let’s start with:
1. Gamma Rays
Gamma rays have the shortest wavelength and the highest energy out of all waves on the electromagnetic spectrum. They have so much energy that they can strongly penetrate any matter and knock out electrons from atoms and molecules of that matter, a process called ionisation. Thus they are also know as ionising radiation. They were discovered by physicist Ernest Rutherford, he won a Nobel Prize in Chemistry in 1908 for his work on gamma rays. Gamma rays can be found in space as gamma ray bursts. Do you know? These bursts of gamma rays can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime!
They cannot reach us as they are absorbed by Earth’s atmosphere. On Earth, however, gamma rays can be produced by lightning and nuclear explosions. Additionally, they are released from many of the radioisotopes found in the natural radiation decay series of uranium, thorium and actinium. Interestingly, naturally occurring radioisotopes potassium-40 and carbon-14 that are found in all rocks and soil and even in our food and water emit gamma radiation. Our bodies are also... slightly radioactive!
1.1 Harmful effects of Gamma radiations:
Ionising radiations are emitted not only at the time of nuclear bomb detonation (Initial Nuclear Radiation) but also for long periods afterward (Residual Nuclear Radiation). The impact of initial nuclear gamma radiation on humans directly depend on radiation dose, that is the amount of radiation absorbed by the body, which is measured in the unit, Gray (Gy). Other factor include that person’s distance from the explosion site. If a person is exposed to 50Gy radiations, the central nervous system will collapse and finally a person will die in 24-48h. When exposed to 10-40 Gy, gastrointestinal death occurs. Between 2-10Gy, bone marrow death occurs which is then followed by multiple short-term (deterioration of skin, lung health, reproductive health) and long-term effects (cancer induction, increased risk of infections, genetic changes). Besides the severe impact of initial radiation, there is lingering health hazards from residual nuclear explosion (radioactive fallout) from weapon debris, fission products, and, in the case of a ground burst, radiated soil. They emit gamma rays for many years and pose health hazards to people nearby.
1.2 Useful effects of Gamma radiations:
Gamma rays at higher doses can kill living cells, but in appropriate small doses they are being used in medicine as a treatment strategy to kill cancerous cells and shrink tumor and to perform most accurate and precise gamma knife radiosurgery on patients with injured brain tissue. It is worth mentioning that, every cancer type has its own sensitivity to radiation. Some cancers, like lymphoma (blood cancer), are very vulnerable to radiation, while others, like soft tissue sarcoma, are relatively resistant. A lot of factors are considered before deciding on the radiation dosing (dose and number of sessions) for each cancer patient. The factors considered for personalising the radiation overall dose includes: 1) goal of the physician (either definitive, adjuvant or palliative treatment plan), 2) type of tumor being treated, 3) the amount of fractionation (splitting the dose) planned, 4) the presence of nearby organs, and 4) whether chemotherapy or immunotherapy is being given at the same time.
Gamma radiations are lethal because they can penetrate all kinds of matter and damage the DNA, blueprint of life. Gamma rays can destroy rapidly dividing cells and hence works well for treatment of cancer but in this process it also kills rapidly dividing healthy cells, like hair follicles, lining of intestine, blood cells and skin. Therefore patients undergoing radiation therapy also have to suffer from all the side-effects of non-specific ionising gamma radiations.
Gamma radiations also find use in medical diagnostic studies: used for brain, bone, liver, spleen and kidney imaging and also used for blood flow studies.
Besides, gamma radiations are also popularly used by food producers to increase the shelf-life of food and drinks. In order to sterilise food products, i.e., to kill all the microorganisms, food products are bombarded with high-energy gamma rays, normally from radioisotopes like Cobalt-60 or Cesium-137. Do you know, Food irradiated by gamma radiations can last for years without spoiling and hence astronauts space foods are preserved by irradiation! Besides food, gamma rays are used for sterilisation of medical equipment in hospitals.
Manufacturers also use industrial radiography, which is based on gamma radiation’s potential to easily penetrate matter and hence see the internal structure of materials without any destruction. In this way these radiography scans helps to detect any defects - flaws or cracks in the pipes, welded materials or airplane parts . They also have use in our homes, gamma emitter radioisotope, americium-241 is used in household smoke detectors.
In summary, controlled and optimal doses of gamma rays have many uses. But, these radiations can’t give you superpowers like Incredible Hulk!, if you wish for that try hitting gym and lifting weights.
2. X-Rays
We all are quite familiar with X-rays, at some point in our life we have been exposed to X-rays either for broken or fractured bone(s), at dentist’s clinic or for lungs, heart or breasts scan. X-rays are indispensable diagnostic tool in modern medicine. X-rays were discovered by physicist Wilhelm Conrad Röntgen, who won the first Nobel Prize for Physics, in 1901. Discovery of X-rays were labeled a medical miracle.
Do you know? Discovery of X-rays was a fortunate stroke of serendipity. Because Röntgen did not knew the nature of these rays, he dubbed them as X-rays or Unknown rays.
2.1 Harmful effects of X-Rays:
Like gamma rays, X-rays are ionising in nature, can penetrate matter but unlike gamma rays their energy levels are much lower. Such unique properties of X-rays helped in significant scientific advancement that ultimately benefited a variety of fields, most of all medicine, by making the invisible visible. However, if not used cautiously, that is, without optimising dose and minimising unnecessary exposure, X-rays can cause deleterious side-effects like burns and damage of skin and also skin cancer. These deleterious effects are similar to the ones discussed in harmful effects of gamma radiation (Section 1.1), collectively referred to as radiation poisoning.
2.2 Useful effects of X-Rays:
But now with better understanding of the risks associated with X-ray radiation, clinicians have developed protocols to greatly minimize unnecessary exposure. X-rays are used in many ways: 1) Standard X-ray to easily differentiate between bone and soft tissue ; 2) Contrast X-ray scans can be used to further differentiate areas of soft tissue; 3) Mammography to scan breasts for any early signs of breast cancer; 4) Fluoroscopy can obtain real-time images of movement within the body or to view diagnostic processes; 5) Computed tomography (CT) scans which combines traditional X-ray technology with computer processing to generate a series of cross-sectional images of the body that can later be combined to form a three-dimensional X-ray image. CT scans produces detailed high-resolution (more sensitive) images of internal organs and structures.
Besides their ubiquitous use in medical diagnosis, they also help chemists and biologists to determine the crystal structure in inorganic, organic, and biological materials. X-ray diffraction techniques (or “X-ray crystallography”) is employed for such work. This technique was used by Rosalind Franklin to understand the structure of DNA (famous Photo 51), which facilitated the discovery of the DNA double helix.
As discussed before X-rays are ionising radiations, and they can damage DNA of fast dividing cells, therefore X-rays also find their use in therapeutics to treat cancer, especially blood cancer like leukaemia. Therapeutic radiation can come from a machine outside of the body (localised treatment) or from a radioactive material that is placed in the body, inside or near tumor cells, or injected into the blood stream. X-rays are also used for sterilisation and preservation of food and drinks.
To sum up this section on X-rays, with no hesitance we can say that potential benefits of X-rays outweighs its associated risks. Not a bad legacy for an accidental discovery !
3. Ultra-Violet (UV) rays
You all must have heard about potential hazards associated with UV rays, mostly around summer time, vacation at the beach, on sunscreen bottles/sprays etc. Here we will go little deeper to understand how UV rays does what it does ? Also we will explore the not so known uses of UV rays.
UV rays were discovered by German physicist Johann Wilhelm Ritter in 1801, he called them "(de-)oxidizing rays". Later their name were changed to chemical rays and finally to ultraviolet rays which means ‘beyond violet’.
UV rays are released by Sun and constitutes about 10% of Sun’s total EMR output. They can be broadly divided into 3 categories: UVA, UVB and UVC, depending upon their wavelength range. All UVC and most of UVB rays are absorbed by ozone layer of Earth’s stratosphere. The UV rays which reach us is mix of 95% UVA and 5% UVB. Other sources of UV rays are electric arcs and specialised lights, such as mercury-vapor lamps, tanning lamps, and black lights.
UV rays are not considered as ionising radiation, because its photons lack energy to ionise atoms, however they can interact with organic molecules and can cause chemical reactions. The first interaction of UV rays happens with melanin, a pigment present in melanocytes. Melanocytes are huge cells, shaped like octopus and present in the deep layer of skin. Melanin is also present in eyes, inner ear, vaginal epithelium, meninges, bones, and heart. Melanin gives your skin colour, more melanin means more darker skin tone. Melanin also is the first line of defence from harmful UV rays, it absorbs all the UV rays that can do serious skin damage. If you are under sun for long, you will either get tanned or burned depending upon the melanin content of your skin. Tanned if higher melanin (dark skin tone) and burnt if low melanin (pale skin tone). Sunburn is damage to the skin. It causes pain, redness, and blistering.
Here is how different UV rays are absorbed by our skin:
UVA: can penetrate deep into our skin (dermis). This can cause immediate tanning and premature skin aging, and play a role in the development of certain skin cancers.
UVB can just penetrate the outer protective layer of the skin and is responsible for delayed tanning, sunburns and most skin cancers.
UVC is artificially created to kill bacteria, viruses and fungal spores.
3.1 Harmful effects of UV rays:
Skin cancer: When the energy from UV radiation is absorbed by DNA, it can cause reactions that lead to genetic mutations. These mutations than lead to skin cancers, more commonly seen in older people. Skin damage from the sun starts at an early age and builds up over time. Therefore, protection should start in childhood to prevent skin cancer later in life.
Premature aging of the skin (photoaging): Skin exposed to UV rays can become thick and leathery over time. Sun damaged skin will show earlier-than-normal freckling, wrinkling, loss of collagen, and widening of small blood vessels. These changes start happening from young age and appear around mid 30s or more quickly in people who regularly spend a lot of time in the sun or regularly use tanning beds or lamps. The skin may also develop brown spots (liver spots) in later years.
Cataracts and other eye problems. UV radiation exposure increases the risk of cataracts. This is when the lens of the eye becomes cloudy, making it hard for you to see. If not treated, cataracts can lead to blindness over time. Other eye changes from UV light can include eye damage, eye pain, and vision problems.
3.2 Useful effects of UV rays:
Vitamin D production: The sun's UVB rays interact with a protein called 7-DHC (7-dehydrocholesterol) in the skin, converting it into vitamin D3, the active form of vitamin D. Deficiency of Vitamin D can cause growth retardation and rickets in children that will precipitate and exacerbate osteopenia, osteoporosis and increase risk of fracture in adults. Vitamin D is critical to maintaining bone density by increasing calcium absorption in the gut. Apart from its effects on bone, vitamin D has also been shown to improve balance and muscle strength in the elderly, which decreases the number of falls leading to fracture.
More than 50% of world’s population has low Vitamin D levels, more severely affecting people with high melanin content. Melanin protects from harmful UV rays by absorbing them and thus leaving very little for the production of Vit D.
Mood Levels: UVB helps in the production of Vitamin D which is also a precursor for a neurotransmitter called serotonin. Serotonin is thought to provide sensations of happiness, well-being and serenity to human beings.
Treatment of Skin Conditions: Modern phototherapy uses UV rays to treat certain skin conditions like psoriasis, eczema, jaundice, vitiligo, atopic dermatitis, and localized scleroderma. In addition, UVB, has been shown to induce cell cycle arrest in skin cell. As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and exfoliative cheilitis, conditions in which skin cells divide more rapidly than usual or necessary.
Mating behaviour: UVB exposure can increase the mating behaviour in both males and females by increasing the levels of sex hormones. It was also observed that UVB exposure increased fertility and chances of getting pregnant by increasing the maturation of egg follicles.
UVB radiation can also effectively treat patients with mild hypertension.
Conclusion: Practically, we cannot escape from the effects of UV radiations as they are part of our atmosphere. With thinning of ozone layer, climate change a lot more amount of these rays can travel to us. If we want UV rays to be our friend and not foe, we must diligently practice ways to protect us from over-exposure.
List of science based tools
Employ them to limit the harmful effects of UV rays:
Limit time in midday sun. The sun's rays are strongest between 10 a.m. and 4 p.m. Limit exposure to the sun during these hours, even in winter and especially at higher altitudes.
Use extra caution near water, snow and sand. These three materials reflect the damaging rays of the sun, which can increase your chance of sunburn.
Always use sunscreen. Apply a broad-spectrum sunscreen with a SPF of 30 or higher on all exposed skin 20 minutes before going outside. Reapply every two hours, or after working, swimming, playing or exercising outdoors. Use physical sunscreens instead of chemical sunscreens.
Use hats, sunglasses with UV protection.
Keep track of the UV Index (UVI). UVI is an official forecast from the National Weather Service. It ranges from 0 (low risk) to 11+ (extreme risk).
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