Studies Show Vitamin D Can Reduce Risk of Hospitalization from Respiratory Infections

• Demographics at risk — The researchers noted that middle- and older-aged adults are at a higher risk of these conditions.⁸ Lead researcher Abi Bournot, Ph.D., argues that supplementation can help:⁹

“Supplementation of the vitamin, especially in the winter months when our exposure to sunlight is limited, is an effective way of increasing vitamin D and reducing the risk of serious respiratory tract infections. This is particularly important for older people who are at higher risk of death from such infections, and ethnic minority communities in the U.K., who are at a higher risk of vitamin D deficiency.”

• The impact of vitamin D levels on hospitalization rates — The researchers took existing vitamin D levels and hospital admission records from the dataset and used different analytical models to determine the connection between the two.

Participants with serum vitamin D levels below 15 nanomoles per liter (nmol/L) had a 33% risk of hospitalization compared to adults with an average vitamin D level of 75 nmol/L or more. Note that this is the unit of measurement for U.K. In America, 75 nmol/L is equivalent to 30 nanograms per milliliter (ng/mL).

• A look at other vitamin D ranges — Findings show that vitamin D levels above 15 nmol/L (6 ng/mL) generally had lower hospitalization rates. For example, those who had an intermediate range (15 to 74 nmol/L; 6 to 29.6 ng/mL) “were not associated with a statistically significant increase in risk.” Moreover, every increase of 10 nmol/L (4 ng/mL) in serum vitamin D was linked to a generally significant reduction in hospitalizations.¹⁰

“Our findings of a significant association between increased vitamin D levels in our bodies and reduced hospital admission rates warrants further study, and points to the potential for vitamin D supplementation and consumption of vitamin D fortified foods to reduce the risk of hospitalization with respiratory infections in the future, and therefore mitigate pressures on the NHS (National Health Service),” The researchers noted.¹¹

• Key findings of the study — The researchers reported that daily dosing produced a statistically significant reduction in acute respiratory infection risk, with a 16% lower risk of developing a respiratory tract infection compared with those who took a placebo.

However, bolus dosing — giving vitamin D in large, intermittent doses — did not have this effect. Only daily intake produced an advantage.

• Certain subgroups improved more than others — The researchers reported that baseline vitamin D status, age, and dose size did not significantly modify the overall statistical outcome at the meta-analysis level, but the subgroup that showed clear significance was, again, the daily intake group. This shows that the frequency of intake plays an important role in determining the impact of vitamin D on your health.

Another point worth noting is how consistent the findings were across different populations in the daily dosing subgroup. Whether participants were young, older, living with chronic illness, or generally healthy, the protective effect remained statistically reliable inside the daily-dose category. That means your background health status does not prevent you from gaining protection by vitamin D. Again, the main factor depends on a steady intake to support your immune system.

• A look at the safety outcomes — Serious adverse events were almost identical between vitamin D and placebo with an odds ratio of 0.96, which means that there is no meaningful increase in safety concerns from supplementation. Thus, there are close to no downsides when boosting your vitamin D levels.

• Daily dosing produced a measurable improvement — The study reported “significant preventive effects of vitamin D supplementation” for daily users. This means that integrating vitamin D optimization into your routine every day offers a noticeable advantage. Even short-duration trials produced positive results.

• Group-specific effects — Exploring group-specific effects revealed even more insights. For example, daily dosing helped people across a wide age range, but the greatest benefits showed up in groups exposed to seasonal shortages of sunlight and those living in regions with long winter cycles. These are demographics most likely to face prolonged vitamin D insufficiency.

• The downside of bolus dosing — Similar to the previous study, this one also investigated bolus dosing and found similar results. Across the selected dataset, irregular dosing frequencies consistently failed to show significant benefit.

1. Make sunlight your main vitamin D source — Your skin produces vitamin D the moment sunlight hits it. To maximize vitamin D production, expose as much skin as practical — arms and legs at minimum, torso if privacy allows. More skin surface means more vitamin D synthesis in less time, reducing your UV exposure while achieving the same benefit.

Now, how do you know if you’ve produced enough vitamin D for the day? If you notice redness or burning, you’ve gone past your safe limit. When your skin tone looks unchanged, you’re still within a safe range. This built-in feedback mechanism accounts for the current season, your latitude, and your natural skin pigmentation. However, before heading out, it’s important to read the next point.

2. Clear vegetable oils from your diet before ramping up sun exposure — As mentioned earlier, sunlight is the ideal way to produce vitamin D. However, if your diet has included canola, soybean, sunflower, safflower, or other seed oils, the linoleic acid (LA) from them has already built up in your tissues.

When LA absorbs ultraviolet light, it oxidizes, drives inflammation, and damages DNA. It also increases your sunburn risk, especially during the midday window when the ultraviolet B rays required for vitamin D production are strongest. To protect yourself, start by lowering your LA intake below 5 grams per day, and swap seed oils for traditional animal fats like tallow, ghee, or grass fed butter. If you can get it below 2 grams per day, that’s even better.

To help you track your daily LA intake, sign up for the upcoming Mercola Health Coach app. It contains a feature called the Seed Oil Sleuth, which calculates the LA in your food down to a tenth of a gram. This makes it far easier to stay within a healthy range.

Note that your body needs about six months of avoidance from seed oils to start clearing LA from tissues. As LA levels fall, your skin becomes more resilient to sunlight, and your sunburn threshold rises. This also increases your ability to safely benefit from midday sunlight.

Here’s another helpful tip — take C15:0 (pentadecanoic acid), which is normally found in grass fed dairy. In a previous article, I went into detail into how it accelerates the removal of LA from tissues.

3. Choose vitamin D3, and pair it with magnesium and K2 — If you need to take a supplement, choose D3 — this is the same form your skin makes. Interestingly, taking D2 reduces the availability of usable D3, disrupting the balance you’re trying to restore. To make D3 work properly, support it with magnesium and vitamin K2. Magnesium activates vitamin D so your tissues can use it, and K2 ensures that calcium moves into your bones instead of settling in arteries or other soft tissues.

These nutrients operate as a team. Without magnesium and K2, your body struggles to activate vitamin D, forcing you to take higher doses just to achieve the same effect. That approach creates more problems than it solves, specifically vitamin D toxicity.

4. Test your vitamin D levels twice a year — Knowing your baseline is important. So, I recommend keeping your vitamin D level between 60 and 80 ng/mL. If your results fall short, refocus on lowering your LA intake and gradually increasing safe sun exposure. Done right, you won’t even have the need to spend on supplements. Regular testing also helps you adjust your approach over time, ensuring that your strategy matches your actual physiology, so you’re not guessing all the time.