Medically Reviewed by Mahammad Juber, MD on February 26, 2022
Lack of Sleep

Lack of Sleep


Not getting enough sleep can make you more likely to catch viruses or germs.  And you also may take longer to get better. That’s because your body can’t make as many infection-fighting cells and proteins called antibodies that help defend against illness. Your body releases certain proteins that help the immune system, called cytokines, only during sleep. 




Stress and worry aren’t great germ fighters. Just having anxious thoughts can weaken your immune response in as little as 30 minutes. Constant stress takes an even bigger toll and makes it harder to fend off the flu, herpes, shingles, and other viruses. Talk to your doctor if you can’t shake your worry or if it gets in the way of normal life.

Low Vitamin D

Low Vitamin D


You may know you need it for strong bones and healthy blood cells. But vitamin D also helps boost your immune system. You can get it in eggs, fatty fish, and fortified foods like milk and cereal. Sunlight is another key source. In the summer, just 5-15 minutes of rays on your hands, face, and arms 2-3 times a week usually is enough. In the winter, you might need a bit more.

Certain Medications

Certain Medications


They include drugs to treat allergies, arthritis, lupus, IBS, and organ transplant.  Corticosteroids are one example, as are TNF inhibitors for inflammation and chemotherapy for cancer. Talk with your doctor before you adjust any prescription medication. 

Too Few Fruits and Veggies

Too Few Fruits and Veggies


These foods may help your body make more of the white blood cells you need to fight off infections. Fresh produce and nuts and seeds pack a lot of zinc, beta-carotene, vitamins A, C, and E, and other nutrients you need for a healthy body. Plant-based foods also fill you up with fiber, which helps lower your body fat percentage, which can strengthen your immune response. 




Smoke from pot can inflame your lungs. If you use it regularly, you may have the same breathing problems you can get from nicotine cigarettes. That means coughing up colored mucus called phlegm and a higher chance of lung infections.  

High-Fat Diet

High-Fat Diet


Oils can hinder germ-fighting white blood cells. And high fat diets over time can upset the balance of bacteria in your gut that can help immune response. Look for low-fat dairy with no added sugar, along with lean protein like seafood, turkey, and chicken, or lean cuts of beef with any visible fat cut off. Also, being obese seems to make you more likely to get the flu and other infections, like pneumonia.

Too Little Time Outdoors

Too Little Time Outdoors


Sunlight may energize special cells in your immune system called T-cells that help fight infection. But being outside brings other benefits, too. Many plants in the woods make phytoncides and other substances you breathe in that seem to bolster your immune function.




Nicotine from cigarettes, chewing tobacco, or any other source can weaken your body’s ability to fight germs. Yes, vaping counts, too. And it’s not just the nicotine. Other chemicals in e-liquids seem to suppress your immune response, especially when you inhale them through vaping.




Just overdoing it once slows your body’s ability to fight germs for up to 24 hours. Over time, drinking too much blunts your body’s ability repair itself. That may be part of the reason you’re more likely to get illnesses like liver disease, pneumonia, tuberculosis, and certain cancers. If you use alcohol, try to keep it to one drink a day for women and two drinks for men.




There is some evidence that sorrow, especially if lasts a long time, can depress your body’s immunity. The effect can linger for 6 months, but may go on longer if your grief is deep or doesn’t ease. Talk to your doctor or a mental health professional if you need help with a loss or traumatic event.

Lack of Exercise

Lack of Exercise


Regular aerobic exercise appears to help your body fight illness caused by viruses and bacteria. That’s in part because it helps blood get around your body more efficiently, which means germ-fighting substances get where they need to go. Scientists continue to study exactly how exercise helps boost your immune system.

No Sex

No Sex


Good news! Weekly intimacy seems to help boost your immune system compared to those who have it less often. Sex raises levels of a germ-fighting substance called Immunoglobulin A, or IgA. But more may not always better. Couples who had sex more than twice a week had lower levels of IgA than those who had no sex at all.

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Academy of Nutrition and Dietetics: “Support Your Health With Nutrition.”

Alcohol Research: “Alcohol and the Immune System.”

American Academy of Family Physicians: “Health Benefits of a Good Sex Life.”

American Council on Exercise: “Get Out! 5 Benefits of Outdoor Exercise.”

American Psychological Association: “Stress Weakens the Immune System.”

American College of Rheumatology: “TNF Inhibitors.”

BMJ Journals Thorax: “Pro-inflammatory effects of e-cigarette vapour condensate on human alveolar macrophages.” “How Chemotherapy Affects the Immune System.”

British National Health Service: “Benefits of love and sex.”

CDC: “Alcohol and Public Health,” “Marijuana and Public Health,” “Medications that Weaken Your Immune System and Fungal Infections.”

Cleveland Clinic: “6 Surprising Ways Alcohol Affects Your Health — Not Just Your Liver,” “FAQs: What You Should Know About COVID-19 and Chronic Medical Conditions.”

Dialogues in Clinical Neuroscience: “Physiological correlates of bereavement and the impact of bereavement interventions.”

Frontiers in Immunology: “Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan.”

Frontiers in Psychology: “How might contact with nature promote human health? Promising mechanisms and a possible central pathway.”

Georgetown University Medical Center: “Sunlight Offers Surprise Benefit – It Energizes Infection Fighting T Cells.”

Harvard Health Publishing: “How to boost your immune system,” “Grief can hurt — in more ways than one,” “A prescription for better health: go alfresco.”

Harvard Medical School Division of Sleep Medicine: “Sleep and Disease Risk.”

Indian Journal of Medical and Paediatric Oncology: “Harmful effects of nicotine.”

Mayo Clinic: “Lack of sleep: Can it make you sick?”

National Cancer Institute: “Vitamin D and Cancer Prevention.”

National Kidney Foundation: “Immunosuppressants.”

National Institute on Alcohol Abuse and Alcoholism: “Alcohol's Effects on the Body.”

National Institute on Drug Abuse: “What are marijuana's effects on lung health?”

National Office of Dietary Supplements: “Vitamin D.”

New England Journal of Medicine: “Adverse Health Effects of Marijuana Use.”

Oxidative Medicine and Cellular Longevity: “High anxiety

Recognizing stress as the stressor.”

Public Health Review: “Anxiety and Depression: Linkages with Viral Diseases.”

Physicians Committee for Responsible Medicine: “Foods To Boost the Immune System.”

PlosONE: “Exposure to Electronic Cigarettes Impairs Pulmonary Anti-Bacterial and Anti-Viral Defenses in a Mouse Model.”

Psychological Reports: “Sexual frequency and salivary immunoglobulin A (IgA).”

Psychosomatic Medicine: “A Systematic Review of the Association Between Bereavement and Biomarkers of Immune Function.”

World Health Organization: “Ultraviolet radiation (UV).”