Why Immunity Drops in Winter
Our nutritionist, Jennie Carolan, Masters in Food Science & Nutrition, recently shared a guide to the winter season for those in the 12 Week Nutrition Challenge. She always packs powerful and insightful information into each week, so we wanted to share this one with everyone so you can thrive this winter.
People tend to get sick more often during the colder months for several reasons.
Indoor time increases exposure. More time inside in close proximity makes respiratory droplets easier to spread.
Cold, dry air helps viruses survive. Dry indoor heat and cold outdoor temperatures create an environment where viruses stay active longer.
Less sunlight lowers vitamin D. Lower vitamin D weakens immune cell activity. Research shows vitamin D plays a major role in regulating immune responses and reducing the risk of respiratory infections (Martineau et al., BMJ, 2017).
Sleep quality often worsens. Holiday stress and disrupted routines reduce nightly repair. Adults who sleep fewer than six hours per night are significantly more likely to catch a cold than those who sleep at least seven hours (Prather et al., 2015).
Protein and the Immune System
Protein provides the amino acids your body uses to build antibodies, immune cells, and repair tissues. Low protein intake weakens both innate and adaptive immunity (Li et al., 2018). Hitting your protein target at each meal is one of the most effective ways to support your immune system. Core Four balanced plates help maintain steady intake throughout the day.
If you’d like help building balanced meals or dialing in your macros, check out our nutrition services: APEX PWR Nutrition Services or try our one-time macro evaluation: One-Time Macro Count.
Fiber and Gut Health
About seventy percent of your immune system lives in the gut. The gut microbiome influences how efficiently immune cells respond. Fiber feeds the beneficial bacteria that support this process. Fruits, vegetables, beans, whole grains, chia seeds, flaxseed, and lentils all play a role. A diverse, fiber-rich diet improves immunity by strengthening gut microbial diversity (Zmora et al., 2018). Fiber also helps regulate inflammation, which is especially important during winter months.
Vitamin C and Antioxidants
Vitamin C does not prevent colds, but it can shorten the duration and reduce symptom severity. It supports immune cell function and helps reduce oxidative stress. A Cochrane review of more than eleven thousand participants found that vitamin C supplementation reduced cold duration, especially in physically active individuals (Hemilä and Chalker, 2013). Consistent intake through whole foods is more helpful than megadoses. If you want to add supplementation, our favorite Vitamin C product is by Thorne. Click here to get 25% off this and more!
Great sources include citrus fruits, berries, bell peppers, kiwi, tomatoes, and broccoli.
Vitamin D and Winter Immunity
Vitamin D is one of the most studied nutrients for immune health. Low levels are linked to a higher risk of respiratory infections. Sunlight is the primary source, but winter reduces natural production. Some foods contain vitamin D such as fatty fish, egg yolks, and fortified dairy or plant milks. Supplementation may help if levels are low. The BMJ meta-analysis by Martineau et al. shows that vitamin D supplementation reduced the risk of acute respiratory infections, especially in people who were deficient. If you feel like supplementation is necessary, get one of Thorne’s many different Vitamin D supplements (different doses) at 25% off – click here.
Zinc and Immune Function
Zinc supports the development of immune cells and can help shorten the duration of cold symptoms when taken at the onset of illness. Good sources include beef, poultry, beans, nuts, seeds, and yogurt. Zinc lozenges taken early reduced cold duration by about thirty-three percent in a review published in the Journal of Infectious Diseases (Hemilä, 2017). Zinc is helpful at first symptoms but should not be taken daily in high amounts.
Hydration and Mucosal Defense
Dry winter air pulls moisture from the body and from the mucosal lining of the nose and throat. This lining serves as one of the first defenses against viruses. Proper hydration keeps it functioning effectively. Research shows dehydration impairs mucosal immunity and increases susceptibility to respiratory infections (Popkin et al., 2010). Set a hydration target and stay consistent through the winter.
Sugar, Alcohol, and Immune Stress
Higher sugar intake and more frequent alcohol consumption during the holidays can disrupt immune function. Sugar contributes to inflammation and blood sugar swings. Alcohol disrupts sleep, increases liver stress, and temporarily lowers immune efficiency. The key is balance. This is not about perfection. It is about being intentional in a season when indulgences naturally increase.
Practical Steps for Stronger Winter Immunity
- Prioritize protein at every meal
• Aim for at least two to three servings of fruits and vegetables daily
• Include probiotic-rich foods such as yogurt, kefir, kimchi, or sauerkraut
• Maintain adequate vitamin D through food or supplementation
• Set a daily hydration target
• Keep alcohol mindful and intentional
• Build Core Four plates rather than grazing
• Prioritize sleep and consistent routines
• Increase movement even with shorter days
If you’d like structured support from meal planning to supplement recommendations, check out our coaching and nutrition programs:
APEX PWR 12-Week Nutrition Challenge or The Power of Nutrition Coaching.
Need high-quality supplements? APEX partners with Thorne so you can get trusted, clean formulas with a lifetime discount: Explore Thorne at APEX PWR.
Goals for This Week
- Prioritize protein at each meal with consistent Core Four plates
• Increase fiber by adding one fruit and one vegetable daily
• Stay within macro ranges at least five days this week
• Keep hydration above seventy-two ounces
• Limit alcohol to intentional occasions and track it clearly
• Plan dinners in advance and send menus if you want help
• Add ten to fifteen minutes of extra movement daily to increase NEAT
Check-In Prompts
- How were hunger, energy, sleep, and digestion this week?
• Did meals feel structured or did snacking increase?
• Did you meet your protein and fiber goals on most days?
• How many days did you fully track food from morning to night?
• What stressors or challenges made the week difficult?
• What felt easier compared to last week?
• How can I support you this coming week?
Recipe of the Week: High Protein Winter Immunity Bowl
Ingredients
• 1 cooked chicken breast, shredded
• 1 cup shredded kale
• 1 cup roasted sweet potato
• 1 mandarin orange, segmented
• 1 tablespoon pumpkin seeds
• 2 tablespoons diced red onion
• 1 tablespoon olive oil
• 1 tablespoon lemon juice
• Salt and pepper to taste
Instructions
- Combine kale and roasted sweet potatoes in a bowl
- Add shredded chicken and mandarin orange segments
- Sprinkle pumpkin seeds and red onion on top
- Drizzle with olive oil and lemon juice
- Season with salt and pepper, toss gently
- Enjoy warm or chilled
This nutrient-dense meal combines lean protein, fiber, healthy fats, vitamin C, and antioxidants, all key ingredients for supporting immune function through winter.
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