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Smoking remains one of the biggest causes of preventable deaths globally. According to the Centers for Disease Control and Prevention (CDC), smoking accounts for 1 in about five deaths in the United States every year.
As of 2019, 14% of the adult population in the country are smokers.
The American Lung Association states that there are more than 600 ingredients present in a cigarette. Each cigarette releases about 7000 chemicals when it is burnt. Out of these, close to 70 chemicals are proven carcinogens (cancer-causing substances). Some of them are:
When a person inhales cigarette smoke, these carcinogens and other chemicals reach the lungs and are distributed throughout the body.
Once these carcinogenic chemicals enter the body, they are detoxified by the cytochrome P450 group of enzymes (CYPs).
These CYP enzymes convert these carcinogens into a more active intermediary form called DNA adducts. DNA adducts are parts of the DNA that attach themself to these cancer-causing chemicals.
The intermediaries lead to DNA damage and abnormal cell multiplication and have to be quickly detoxified by other enzymatic processes. Unfortunately, in some people, the number of cancerous intermediaries builds up at a faster rate than they are eliminated. This leads to cancer.
There are other carcinogens in cigarette smoke that directly form DNA adducts without the help of the CYP enzymes. These lead to direct DNA damage and cell abnormalities, and resultant cancer.
While smoking is a risk factor for all types of cancer, it is significantly associated with breast cancer in women.
In the United States, 1 in every eight women will be diagnosed with breast cancer in her lifetime. Smoking increases this risk drastically.
A study published in the BioMed Central Ltd forum analyzed the risk of breast cancer in women who smoked.
102,927 women were chosen and monitored for 7.7 years. In the end, 1815 women developed invasive breast cancer. The study found that smokers had a 14% higher risk of developing breast cancer than non-smokers.
Learn More: How Genes Influence Your Risk for Nicotine Dependence?
This study also mentions that women who start smoking before 17 had a significantly higher risk (24%) for breast cancer.
Another study analyzed the risk of breast cancer in 111,140 active smokers and 36,017 passive smokers (people who don’t smoke themselves but are exposed to other people’s cigarette smoke).
According to the study, some factors that increase the risk of breast cancer are:
Secondhand smoke is also called passive smoking and is smoke that a person inhales unintentionally. For example, people can inhale tobacco smoke by just being around others who smoke. According to the California Air Resources Board, secondhand smoke is a proven carcinogen.
The smoke that is released from the burning ends of cigarettes is called sidestream smoke. Sidestream smoke is unfiltered and hence contains more harmful substances than the smoke that a smoker breathes out.
A 2013 study analyzed the risk of breast cancer in 322,988 active, passive, and non-smokers.
Compared to non-smoking women, those exposed to passive smoke at home or work had a higher risk of developing breast cancer.
The GSTM1 gene (glutathione S-transferase mu 1 gene) helps produce the glutathione S-transferase enzyme that belongs to the Mu class. The Mu class of enzymes helps in eliminating carcinogens and other environmental toxins from the body.
rs366631 is a single nucleotide polymorphism or SNP in the GSTM1 gene.
People with the GSTM1 null genotype have a higher risk of developing breast cancer when exposed to cigarette smoke.
Null genotype is the non-functional variant of the gene that results in total loss of function of the gene.
Here, the TT genotype is the null genotype.
The risk of breast cancer was also more severe in postmenopausal smokers with the GSTM1 null genotype.
| Genotype | Implication |
| TT | Increased risk of breast cancer upon smoking |
| CT | Normal risk of breast cancer upon smoking |
| CC | Normal risk of breast cancer upon smoking |
The SLC4A7 gene (Solute Carrier Family 4 Member 7 gene) helps produce a protein that transports sodium and bicarbonate ions. It also plays a role in the metabolism of different acids, ions, and amine compounds.
rs4973768 is an SNP in the SLC4A7 gene. A meta-analysis has reported an increased risk for breast cancer upon smoking in T allele carriers.
| Genotype | Implication |
| TT | Increased risk of breast cancer upon smoking |
| CT | Increased risk of breast cancer upon smoking |
| CC | Normal risk of breast cancer upon smoking |
There are so many government and private bodies that help people with tobacco addiction. You can get help from some of these rehab centers to stop or limit smoking. It takes time and effort to curb the craving. Here are some pointers that can help you with this.
For people who have been smoking for years together, some places, smells, habits, or environments can create an urge to smoke. Understand these triggers and stay away from them. Practice the below activities to make quitting smoking easier.
Secondhand smoking ends up harmful to non-smokers. Here are ways you can limit/eliminate secondhand smoke exposure.
Genetic testing helps identify genetic factors that could increase your breast cancer risk. If you do have a high genetic risk, regular screening may help.
Did you know that our ancestors were nocturnal? They used to stay awake in the night to hunt without worrying about dangerous predators and sleep during the day. Now, our circadian rhythms are lined up with the sun. That's why as soon as the sun sets, our bodies start getting ready for rest, and we end up feeling sleepy.
Circadian rhythms are biological cycles that coordinate essential mental and physical functions, such as sleep and hunger. The circadian clock is regulated by a part of the brain called the Suprachiasmatic Nucleus (SCN).
The circadian clock is also influenced by temperature. When the body temperature drops around the afternoon and late evening, it induces drowsiness and sleep.
Sleep is induced by a hormone called melatonin, which is produced in low-light conditions. Bright light conditions during the day suppress melatonin production and promote wakefulness.
People who work the night shift have disrupted circadian rhythm and have an increased risk for the following conditions:
Working the night shift is carcinogenic to humans, according to multiple studies conducted the world over.
Several studies show that disruption in the night’s sleep can reduce melatonin levels and increase the risk of tumor growth.
Some animal studies have shown that exposure to light at night led to the growth of breast cancer.
The risk of breast cancer among nurses and other night-shift workers seems to be higher than their counterparts who worked day shifts.
A study published in the Journal of National Cancer Institute in 2001 reported that women who work in rotating night shifts for at least three nights per month, along with day shifts, have a moderately high risk of breast cancer.
Further, the risk seems to be higher when the night shifts per week increase!
This increased risk is attributed to the messed-up melatonin levels in the body.
In addition to promoting sleep, melatonin also stops tumor growth and protects against the spread of cancer cells.
When melatonin levels decrease in the body, it results in an imbalance of inflammatory cytokines, increased mutations in the cells, and oxidative damage (due to free radicals).
These events can all trigger cancer development.
A reduction in melatonin also affects estrogen levels, which further increases the risk of breast cancer.
A long duration of shift work throughout the years is associated with estrogen and progesterone-positive tumors.
When the circadian rhythm is altered, it changes the expression of the CLOCK genes. This also influences the production of reproductive hormones.
The Neuronal PAS Domain Protein 2 or NPAS2 gene is the largest circadian gene. It plays a vital role in sleep homeostasis and circadian rhythm regulation.
This gene also regulates the cell cycle and works with certain other genes for repairing DNA. The NPAS2 gene shows a strong association with breast cancer.
rs2305160 (Ala394Thr) is an SNP (Single Nucleotide Polymorphism) in the NPAS2 gene.
Among women with little or no exposure to shift work, the A allele (AA or AG) is associated with a significantly lower risk of breast cancer.
However, among women with AA genotype who had worked >2 years of rotating night shifts, the risk of breast cancer was nearly 3 fold compared to women with the same genotype with <2 years of night shift work.
| Genotype | Implication - > 2 years of rotating night shifts |
| AA (Thr/Thr) | ~3 fold increased risk of breast cancer |
| AG (Thr/Ala) | Slightly increased risk of breast cancer |
| GG (Ala/Ala) | Normal risk of breast cancer |
Use Xcode Life’s Free Gene Tool To Find Out If You Have The Risk Genotype!
RAR-Related Orphan Receptor A or the RORA gene is located on chromosome 15 and regulates genes involved in the body’s circadian rhythm.
rs1482057 is an SNP in the RORA gene. A study published in 2014 showed that SNP rs1482057 was associated with breast cancer in postmenopausal women.
Women who have at least one A allele and had a history of working night shifts in their lifetime had a higher risk of developing breast cancer.
Conversely, women having the CC genotype and working night shifts showed a decreased risk of breast cancer.
| Genotype | Implication |
| AA | Increased breast cancer risk on night shift work |
| AC | Increased breast cancer risk on night shift work |
| CC | Decreased breast cancer risk on night shift work |
Cryptochrome circadian regulator 2 or the CRY2 gene gives instructions to produce a protein involved in regulating the body’s circadian rhythm.
rs2292912 is an SNP in the CRY2 gene, located on chromosome 11. Night shift working increased the risk of breast cancer in women who carried the CG genotype of rs2292912 SNP.
| Genotype | Implication |
| CG | Increased breast cancer risk on night shift work |
| GG | Decreased breast cancer risk on night shift work |
| CC | Decreased breast cancer risk on night shift work |
Since working night shift hours increases the risk of breast cancer in women, one of the most effective ways to lessen this risk is to reduce working night shifts.
Switching with a colleague’s shift, alternating your night shifts with day shifts, or switching jobs can be a few ways by which you can reduce your night shift hours.
Apart from disrupting the sleep-wake cycle, disturbed sleep or poor quality of sleep in people who work night shifts can increase their risk for breast cancer.
So, if you are working a night shift, ensure you get your 7-8 hours of sleep every day. If you have trouble sleeping, consult your doctor about supplements that can help you catch up on your daily sleep.
People working the night shift must try and reduce other risk factors of breast cancer.
A healthy diet with lots of fruits, limited alcohol consumption and smoking, adequate physical activity, and reduced exposure to harmful chemicals can help reduce breast cancer risk.
