Cancer Protection: Are Your Natural Killer Cells on Active Duty?

by , | Last updated Jan 11, 2024 | Cancer, Immune Efficiency

Cancer cells are smart and are adept at hiding from the immune system. So, how does the body fight cancer? There are cancer-destroying immune cells. Virus zapping cells. Yes, we want these white blood cells known as natural killer cells to be effective in their work of protecting us from cancer. Our lifestyle habits either improve or decrease their effectiveness.

How Natural Killer Cells Work

Natural killer (NK) cells, as well as killer-T lymphocytes, are specialized immune cells that kill viruses and combat cancer. They release chemical bullets that perforate the protein coating of viruses and the membranes of cancer cells. Natural killer cells also damage the DNA of cancer cells and interfere with the replication of viruses. Although classified as lymphocytes, they provide non-specific immunity.

NK cells release perforins into the membranes of their target cells. “Perforin” comes from the word “perforate”. So, perforins are a group of chemicals that shoot tiny holes into the membranes of their targets. Special enzymes from the NK cell granules then insert themselves into the target cells through these channels made by perforin. Enzymes, such as fragmentin, cause DNA fragmentation and the death of the target cells. Natural killer cells also exert an antibacterial action against the virus.

Lifestyle Factors That Help or Inhibit NK Cells

Dr. Morimoto and associates at the Osaka University Graduate School of Medicine investigated the association between lifestyle, mental health status, and natural killer (NK) cells. The lifestyle habits they examined included cigarette smoking, alcohol consumption, sleeping hours, working hours, physical exercise, eating breakfast, balanced nutrition, and mental stress. Here is what they discovered: Participants with a good overall lifestyle showed significantly higher NK cell activity than those subjects with poor lifestyle habits. Subjects who complained of an unstable mental status had significantly lower NK cell activity than those who reported having a stable mental status. Consequently, when subjects were divided into four groups by lifestyle and mental health status. Subjects who had poor or moderate lifestyle and reported unstable mental status showed the lowest NK cell activity while subjects who had good lifestyle practices and reported stable mental status showed the highest NK cell activity.1

In a later study, Dr. Morimoto and his colleagues found that healthy lifestyles are associated with higher levels of virus-killing enzymes in natural killer cells as well as significantly higher numbers of NK cells. In contrast, poor lifestyle habits decrease the number of the natural killer cells and their viral-destroying enzymes.2


Aerobic exercise increases the number and efficiency of the natural killer cells. Regular exercise improves resting natural killer activity in the elderly (potentially increasing resistance to both viral infections and prevention of malignant cell formation). Both moderate and strenuous physical exercises cause natural killer cells to be released in the blood. A few hours after moderate exercise the NK cells are back to normal capacity. But following strenuous, exhaustive exercise the number of natural killers is decreased, and their activity is depressed for several days.3


Fasting for short periods of time improves natural killer cell activity. A vegetarian diet increases NK cell activity by a factor of 2.34 compared to an omnivorous diet.4,5 Garlic consumption increases natural killer cell activity. Selenium also helps NK cells to proliferate and increases their activity, too. A diet that has 20-25% of its calories coming from healthy fat sources (nuts, olives, flaxseed, and avocados) beneficially contributes to supporting a maximum functioning of the lymphocyte and natural killer activity.6,7


Temperance is the abstinence from all injurious agents and harmful habits and the moderate use of, or involvement in all good substances and activities. Alcohol suppresses natural killer cell activity.8) Natural killer cell activity is sufficiently lower in alcoholic patients. Patients with a dual diagnosis of either alcohol abuse or secondary depression or depression with a history of alcohol abuse showed a further decrease in NK cell activity compared with that found in patients with either depression or alcoholism alone.

Smoking decreases natural killer cell activity in the lungs;9 cessation of smoking improves it.

Nature Therapy: Spending time in a forest helps to improve stress, improves moods, reduces anger and aggressiveness, and increases overall happiness. Forest visits also strengthen our immune system by increasing the activity and number of natural killer cells that destroy viruses and cancer cells.10 Forest bathing is a short, leisurely visit to a forest. In one study scientists collected samples from individuals who spent a three-day visit to a forest. They calculated mean values on the number and activity of natural killer cells and the stress hormone adrenaline. They found that the number and activity of natural killer cells significantly increased. The number of antiviral and cancer-killing compounds also increased. The effect lasts over 30 days after the visit. Mean values of the concentration of “urinary adrenaline days” were significantly lower after spending three days in the forest.11


Partial sleep deprivation reduces natural killer cell activity per number of natural killer cells. Even a modest sleep deprivation for part of the night can reduce the killing ability of the natural killer cells by almost 30%.12

Mental Attitudes

Mental attitudes significantly influence the efficiency of the NK cells, as well. Early in the last century, health educator Ellen White in her book, The Ministry of Healing, observed, “The relation that exists between the mind and the body is very intimate. When one is affected, the other sympathizes….Grief, anxiety, discontent, remorse, guilt, distrust, all tend to break down the life forces and to invite decay and death.”13

Scientific studies confirm these observations. They show that major depression, for example, reduces NK cells’ effectiveness. A persistent negative outlook erodes both the ability of the NK cells and killer T-lymphocytes to destroy viruses and cancer cells. The emotions and reactive thinking common in depression—helplessness, loneliness, hopelessness, lack of social support, and unhealthy suppression of these feelings—not only depress the mind but the immune system as well.14

Among depressed subjects, those who experienced less subjective control also showed significantly lower NK cell activity. An internal locus of control appears to act as a buffer against the decrease in cellular immunity observed in major depression.15 Depressed individuals who still maintain good executive functioning of the front brain have better immunity than those individuals whose front brain is compromised.

Stress reduces the ability of NK cells to make interferon, a chemical that substantially decreases viral replication. However, problem-solving techniques and coping skills improve NK activity in stressed persons. If the individual possesses high emotional stability and low anxiety, stress actually promotes NK cell activity. On the other hand, the same stress can result in a significant decline in NK cells if the individual possesses high anxiety and low emotional stability.16

Realistic optimism improves NK cells’ ability to perform their job. Ellen White observed that “courage, hope, faith, sympathy, [and] love, promote health and prolong life. A contented mind, a cheerful spirit, is health to the body and strength to the soul.”17 Could this also be true for the immune system? A modern medical journal confirmed this to be so in saying that confidence, openness, social support, effective coping skills, self-discipline, trust, faith, and a will to survive improve NK cells’ efficiency.18

In other words, it is not just stress that shapes your immune system. How you respond has a greater impact.


© 2024, Wildwood Sanitarium. All rights reserved.

Disclaimer: The information in this article is educational and general in nature. Neither Wildwood Lifestyle Center, its entities, nor author intend this article as a substitute for medical diagnosis, counsel, or treatment by a qualified health professional.


  1. Morimoto, K., Lifestyles and mental health status are associated with natural killer cell and lymphokine-activated killer cell activities. Sci Total Environ, 270(1-3):3-11, 2001
  2. Morimoto, K., Li, Q., et al, Healthy lifestyles are associated with higher levels of perforin, granulysin and granzymes A/B-expressing cells in peripheral blood lymphocytes. Prev Med, 44(2):117-23, 2007
  3. Shek, P.N. Strenuous exercise and immunological changes; a multiple-time-point analysis of leukocytes subset CD4/CD8 ratio, immunoglobulin production and NK cell response. Int JSports Med, 16( 7):466-67, 1996
  4. Lau, B. How lifestyle affects the immune system. The Journal of Health and Healing, 16(3):2-6
  5. Malter, M.G. Natural killer cells, vitamins, and other component of vegetarian and omnivorous men. Nutr Cancer, 12:271-278, 1989
  6. Kelley, D.S. Dietary fat and human immune response. Inform, 7:852-58, 1996
  7. Blankenship, J.W., How much fat do we need? The Journal of Health and Healing, 20(1):8-10
  8. Lau, B. How lifestyle affects the immune system. The Journal of Health and Healing, 16(3
  9. Takeuchi, M. Inhibition of lung natural killer cell activity by smoking: the role of alveolar macrophages. International Journal of Thoracic Medicine, 68(3), 2001
  10. USDA Forest Service, Pacific Northwest Research Station. “The healing effects of forests.” ScienceDaily. ScienceDaily, 26 July 2010. www.sciencedaily.com/releases/2010/07/100723161221.htm
  11. Li, Q. Effect of forest bathing trips on human immune function. Environ Health Prev Med. 2010 Jan;15(1):9-17
  12. Irwin, M. Partial sleep deprivation reduces natural killer cell activity in humans, www.psychosomaticmedicine.org/cgi/reprint/56/6/493.pdf
  13. White, E.G. The Ministry of Healing, p. 241
  14. Bergler, R. Psychogenic stimulation of immune system by nutrition. Zentrabl Hyg Unweltmed, 191(2-3):241-64, 1991
  15. Reynaert, C. From health locus of control to immune control: internal locus of control has a buffering effect on natural killer cell activity decrease in major depression, Acta Psychiatr Scand. 92(4), 294-300. 1995
  16. Borella, P. et al, Emotional stability, anxiety, and natural killer activity under examination. Psychoneuroendocrinology, 24(6):13-27, 1979
  17. Ibid. White
  18. Ibid. Bergler

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