The Genetic Link between PTC Tasters and Smoking

By: Karri Lynn Wheat

Latta Jr. High

ABSTRACT

Behavioral scientists spend a great deal of time trying to understand what causes individuals to take up bad habits like smoking. Research suggests that individuals who are able to taste bitter flavors are less likely to smoke since nicotine has a bitter taste. Smoke primarily enters the body through the mouth, therefore, the objective of this project was to determine whether smokers are genetically programmed to be unable to taste some flavors? The hypothesis of this project was that people who smoke will be more likely to not be able to taste the bitterness of PTC papers.

To test this hypothesis, 100 individuals were given a control taste strip with no flavor and a PTC taste strip with a bitter flavor. One hundred individuals were tested: 50 smokers and 50 non smokers. Parental smoking habits were also examined and correlated to their ability to taste the bitter PTC paper. The results supported the hypothesis that smokers were 16 percentage points less likely to taste the bitter flavor found in PTC than nonsmokers. Younger people have a higher taste-sensitivity threshold for PTC than older. The hypothesis was supported because subjects who had no smoker parents could taste the bitter PTC 18.3 percentage points more often than those with the two smoker parents.

INTRODUCTION

Cigarette smoking is the leading cause of preventable death in the United States. At least 500,000 deaths a year occur (3). Smoking cigarettes also contributes to a remarkable number of diseases. These can include strokes, many types of cancer, and coronary heart disease. Smoking directly irritates and causes damage to the respiratory tract. Every year a one-pack-a-day smoker smears the equivalent of a cap of tar over his or her respiratory tract. This can cause a variety of symptoms, including bad breath, cough, and wheezing. They also can cause bronchitis and pneumonia. These effects can heal, but not completely, by quitting. Premature coronary heart disease (CHD) is one of the most important medical consequences of smoking (3). Sadly, sudden death can be the first symptom of CHD and sudden death is four times more likely to develop in a young male smoker than in non-smokers. Women who use both cigarettes and oral contraceptives increase their risk of having CHD. Cerebrovascular accidents (CVA), also known as strokes, cause brain damage that usually leaves its victims with permanent disabilities. Smoking also is a strong risk factor for several types of blood-vessel diseases. It can cause poor circulation to the parts of the body.

Smoking cigarettes damages the body slowly and gradually over a number of years. Virtually everyone knows that smoking is harmful to one’s health and the health of those around you. Health problems such as emphysema, cancer, and heart decease can occur while one is smoking. Some of the damages caused by smoking are irreversible, yet people still choose to smoke. They think that if they quit now it won’t make a difference to the damages that have already happened. That, however, is not true. Even smokers who have smoked for long periods of time would prevent further damage to their body if they would quit.

Smoking may also cause cataracts which may lead to irreversible blindness. A cataract (clouding of the lens) is also another visual problem associated with cigarette smoking. Cigarette smoke irritates the eyes, nose, throat and gums. These certain tissues respond by thickening and by undergoing cellular changes that can eventually lead to mouth, throat, or esophageal cancer. Gum disease can also develop along with tooth loss. Cigarette-smoking can also cause irreversible damage to the larynx. It deepens and hoarseness the voice of a chronic smoker. Women who smoke while pregnant are risking their own lives and their baby’s. Smoking while pregnant can cause stillbirth, miscarriages, and prematurely birth to the baby. Sudden infant death syndrome is significantly associated with smoking, as is impaired lung function at birth. Miscarriage is more common in smokers, as are stillbirth due to fetal oxygen deprivation. Smokers who smoke while pregnant also risk a low weight birth of the baby. Smoking causes premature facial wrinkling through vasoconstriction of the capillaries of the face (3). If scientists could discover what leads so many people to smoking, then possibly the number of smokers could be reduced.

The toxins produced by nicotine enter the body primarily through the mouth. Taste is an important determinant for accepting or rejecting items. Research (4) has shown there is a relationship between smoking and the ability to taste phenylthiocarbamide. Earlier investigations (5) suggest that nontasters may not experience the bitter taste of nicotine in cigarettes and may be at greater risk for prolonged smoking. How individuals are genetically predisposed to respond or not respond to the bitter taste of substances like nicotine may have broad implications for understanding and reducing tobacco use.

Phenylthiocarbamide (PTC) is a chemical compound that has a bitter taste to most people, but some cannot taste it. The ability to taste PTC is inherited, and appears to depend on a pair of genes (2). Individuals having the recessive gene homozygously are nontasters; therefore the ability to taste PTC is a dominant trait. The objective of this project was to determine whether a greater percentage of smokers are genetically programmed to be unable to taste bitter flavors, and thus be more receptive to the flavors in cigarettes. The hypothesis of the project was that people who smoke will be more likely not to taste the bitterness of PTC papers.

METHODS

The materials needed for this experiment included: pencil, paper, 100 control taste papers, which had no taste, and 100 PTC taste papers, which had a bitter taste. The control and PTC taste papers were ordered from Carolina Biological Supply. One hundred participants were sampled. Their ages ranged from ages 16 to 76. Fifty participants were smokers and the other 50 were nonsmokers. Individuals were asked to volunteer to take a simple taste test and answer a few questions. Participants were given 1 control taste paper and asked if they tasted anything. Next, participants were given 1 PTC taste paper and asked if they tasted anything. The following questions and information were taken from each individual:

· Age? Gender? Smoker or nonsmoker?

· Did either of their parents smoke?

· If they were a smoker:

How long had they smoked?

How heavily do they smoke?

(light: < 1 pack/day, medium: 1-2 packs/day, and heavy: >2 packs/day)

RESULTS

Fifty smokers and 50 nonsmokers, for a total of 100 participants, were given the control taste strips and the PTC taste strips. As expected, a small percentage (6%) of the individuals said they detected a taste even on the tasteless strip (Fig. 1). Most individuals, however, taste did not report a taste on the control. Seventy-two percent of all individuals did taste a bitter flavor on the PTC strips, while 28% did not (Fig. 1). This was expected from the research of literature.

Figure 1:

Data Table 1:

Taste Perception on Papers: All Subjects Combined
Total	Number Detecting Taste on Control Paper	Number Detecting Taste on PTC Paper
100	4 (4%)	72 (72%)

Figure 2 shows that the percentage of smokers (64%) who could taste PTC was less than the percentage of nonsmokers (80%).

Figure 2:

Data Table 2:

Smoker/Nonsmoker Differences in Taste Perception
Smoking Habit	Total Number	Number Detecting PTC Taste	%
Nonsmokers	50	40	80.0%
Smokers	50	32	64.0%

Figure 3 breaks down the smokers into the degree of smoking habits. The smokers were classified as light (less than 1 pack per day), medium smokers (1-2 packs a day), and heavy (2 or more packs per day). Thirty-four of the fifty smokers (68%) were classified as medium smokers, nine smokers (18%) were light, and seven (14%) were heavy smokers. This data shows light smokers had the highest percentage of individuals who could taste PTC, and medium smokers had the lowest percentage of individuals who could taste PTC.

Figure 3:

Data Table 3:

Degree of Smoking Habit of Smokers Only
Degree	Total Number 50 (100%)	Number Detecting PTC Taste	%
Light	9 (18%)	8	88.9%
Medium	34 (68%)	19	55.9%
Heavy	7 (14%)	5	71.4%

There was a 7% difference in the percentages of males and females who could taste the PTC, as shown in figure 4. There was some difference in the age groups. Figure 5 shows that people of ages 14 through 45 were more likely to taste PTC than those of ages 46 - 76.

Figure 4

Data Table 4:

Gender Differences in Taste Perception
Gender	Total Number	Number Detecting PTC Taste	%
Males	45	34	75.6%
Females	55	38	69.1%

Figure 5

Data Table 5:

Age Differences in Taste Perception
Age	Total Number	Number Detecting PTC Taste	%
14-29	40	29	72.5%
30-45	28	23	82.1%
46-59	24	16	66.7%
60-76	8	4	50.0%

There was a strong genetic link when the parental smoking habits were examined. The percentage of PTC tasters with no smoking parents was 22.2 percentage points greater than the percentage of PTC tasters with one parent who smoked. It was 18.3% greater than those who had two parents who smoked. This data is shown in figure 6.

Figure 6

Data Table 6:

Parental Smoking Differences and Taste Perception
Number of Parents Who Smoked	Total Number	Number Detecting PTC Taste	%
No Smoker Parents	18	16	88.9%
1 Smoker Parent	48	32	66.7%
2 Smoker Parents	34	24	70.6%

CONCLUSION

The overall data supported the hypothesis that smokers are less likely to taste PTC than nonsmokers. Eighty percent of the nonsmokers could taste PTC while only 64% of the smokers could taste PTC.

The percentages between light, medium, and heavy smokers who could taste PTC was significant. The percentages for the light smokers were higher than the medium smokers (88.9% compared to 55.9%), but 71.4% of the heavy smokers reported being able to taste the PTC papers. When collecting the data, more individuals reported they were medium smokers than light or heavy. Only seven people were classified as heavy smokers. If a larger sample size of heavy smokers was taken then these values would possibly change.

Although research indicated that females were more likely to taste PTC than males this was not supported. Sixty-nine percent of females and 76% of males could taste PTC. The differences are small but present.

There was a difference in age groups who could taste PTC. Younger groups, ages 14 through 45, were more likely to taste PTC than the older groups, ages 46 through 76. Only 50% of those in the 60-76 age group could detect the PTC where as 82.1% of those in the 30-45 age group could. As individuals age it is generally acknowledged that their taste perception decreases. This is the likely reason for the differences in number of individuals in the age groups who could taste PTC.

One very interesting point that supports the hypothesis of the existence of a genetic link was discovered when the subjects who had no smoking parents had a much higher tasting percentage (88.9%) than those who had one (66.7%) or both (70.6%) parents that smoke.

Understanding what motivates people to take up a dangerous health habit like smoking has important health implications. Hopefully, behavioral scientists can come to better understand the physiological and psychological factors that contribute to why people smoke. This could read to the development of improved methods to prevent smoking or help individuals quit smoking.

Possible sources of error might include a larger sample size that could be taken, especially for heavy smokers. It would also be desirable for the age differences of the subjects to have been closer, since younger people have different taste perceptions than older people. To further this project, research could be done by examine the presence or absence of specific genetic markers present the DNA of PTC tasters. Although taste does impact an individual’s choice, role models and environmental factors also influence decisions. This could be yet another avenue to explore.

References

1. Bartoshuk, L. (2000) Comparing Sensory Experiences Across Individuals: Recent Psychophysical Advances Illuminate Genetic Variation in Taste Perception. Chemistry of Senses 25:447-460.

2. Blakeslee, A. F. and Fox, A. L. (1932) Our Different Taste Worlds. Journal of Heredity, 23: 97-107.

3. Brodish, P. (1998) The Irreversible Health Effects of Cigarette Smoking. American Council on Science and Health, June.

4. Kameswaren, L. and Sukumar, M. (1974) Phenylthiocarbamide and Naringin Taste Threshold in South Indian Medical Students. Indian Journal of Pharmaceuticals. 6: 134-140.

5. Fischer, et. al. (1961) Taste Thresholds and Food Dislikes. Nature, 191, 1328.

6. Turnball, B. and Matisoo-Smith, E. (2002) Taste Sensitivity to 6-n-propylthiouracil Predicts Acceptance of Bitter-tasting Spinach in 3-6 year Old Children. American Journal of Clinical Nutrition 76:11101-5.

Acknowledgements

Special thanks go to my mother who helped me analyze my data and prepare my graphs. Also, I would like to thank all those who volunteered to participate in my PTC taste test. Finally, I would like to thank Mrs. Stevens for helping me prepare my Power Point presentation and talk.