Vitamin D3 is a vital nutrient that helps your body absorb calcium, keep bones strong, boost your immune system, and even support sleep and muscle health. Most people don’t get enough vitamin D3 from sunlight during winter, so taking a safe supplement can help. We use this one.
What Are Vitamins, Nutrients, and Vitamin D3?
All vitamins are nutrients, but some are called essential nutrients because you can only get them from food or supplements, not make them yourself. Vitamins and minerals that you only need in tiny amounts are called micronutrients, like magnesium, sodium, vitamin A, and vitamin C. Macronutrients are things like carbohydrates, fats, and proteins, and you need a lot more of those every day.
Vitamin D is a fat-soluble vitamin (meaning it dissolves in fat and gets stored in your body). It comes in two main forms: calcidiol (the “storage” form in your blood) and calcitriol (the “active” form made in your kidneys that helps control calcium use).
Where Does Vitamin D3 Come From?
Your body can make vitamin D3 naturally when your skin is exposed to sunlight. You can also get it from certain foods, like fatty fish or fortified milk, and from supplements. During the summer, outside time can keep your vitamin D levels healthy. But in winter, most people need extra vitamin D from supplements.
Vitamin D and Cellular Aging
A new study suggests that vitamin D may be the closest thing we have to an “anti-aging pill.”
Scientists found that vitamin D regulates genes linked to inflammation, oxidative stress, and cellular aging—three major drivers of the aging process in the body.
In both human and animal studies, individuals with higher vitamin D levels showed fewer markers of aging, less cellular damage, and greater activation of protective genes that help keep tissues youthful and resilient.
This becomes even more important during the winter, when vitamin D levels drop sharply due to reduced sunlight and spending more time indoors. For many people, winter begins with already suboptimal levels, increasing fatigue, recurrent colds, and higher inflammation.
The researchers’ conclusion is clear: maintaining adequate vitamin D levels throughout the winter may be a low-risk, high-reward strategy to support healthy aging—especially when combined with quality sleep, movement, and nutrient-dense foods.
Vitamins and Illness
During a viral illness, taking higher (“mega”) doses of vitamin D3 - together with vitamins K2 MK7 and A - may offer extra support for your immune system. Vitamin D3 helps your body fight viruses by boosting natural defenses and calming down harmful inflammation, which is important when your body is trying to get rid of an infection like the flu or COVID-19. Large doses of vitamin D3 can quickly raise blood levels and help regulate immune responses, while vitamin K2 MK7 works alongside vitamin D3 to ensure calcium goes to the right places and does not build up in arteries or soft tissue. Vitamin A adds even more immune support, because it also helps the immune system fight off germs and keep the linings of your respiratory tract healthy. Several studies show that reaching higher vitamin D3 levels during an infection can reduce the severity of the illness and speed up recovery - especially in people who start out deficient. I use this brand by Adapt Naturals. It’s currently sold out, so I also recommend this other high-quality, highly bioavailable option from NUVASA. When I’m sick, I take 30,000 IU of Vitamin D3 MK7 and 30,000 IU of Vitamin A. Remember, here at Mara Labs, if a supplement already exists in a pure, bioavailable form, we don’t recreate it — we simply recommend it.When I'm sick, I'll take 30,000 IU of vitamin D3 MK7 and 30,000 IUs of Vitamin A. Remember, here at Mara Labs, if a supplement already exists in a pure, bioavailable form, we don't recreate it, we just recommend it!
For more information on our protocol for using large doses of Vitamin D3/K2 for autoimmune, listen to this podcast.
Why Take Vitamin D With K2-MK7?
Vitamin D3 supplements can sometimes cause too much calcium buildup, which can make you feel sick. This is called vitamin D3 toxicity, and it can cause nausea, weakness, and lots of bathroom trips. Taking vitamin D3 with vitamin K2-MK7 helps your body use calcium safely so you don’t have problems. Many people safely take 5,000 to 10,000 IU per day, but it’s best to get advice from your doctor and choose a reliable brand.
Top Five Benefits of Vitamin D3
1. Bone Health:
Vitamin D3 helps your body absorb calcium so you have strong bones and teeth. If levels are too low, bones can become weak or heal slowly. Milk ads often said “Vitamin D does the body good” because of this.
2. Fighting Inflammation and Autoimmunity:
Vitamin D3 can help your immune system work better and reduce inflammation. Some studies show it can help fight diseases where your immune system attacks the body, like multiple sclerosis. Check out this podcast conversation where we discuss this in detail.
3. Better Sleep:
Research shows that vitamin D3 supplements can help improve sleep quality and daytime energy. It even helps kids and teens sleep better and think more clearly.
4. Muscle Strength:
Vitamin D3 helps you build and maintain muscle, and may even help as much as exercising for some people. One study found that vitamin D3 with HMB (a muscle supplement) helped build muscle almost as well as working out.
5. Lower Cancer Risk:
Vitamin D3 can help prevent some cancers and may help people with cancer live longer. While supplements can’t cure cancer, studies show people with healthy vitamin D levels tend to do better.
References
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American Journal of Medicine, 2025 — Study on vitamin D, cellular aging, and inflammation.
https://www.sciencedirect.com/science/article/abs/pii/S0002916525002552? -
"Micronutrients," Wikipedia, https://en.wikipedia.org/wiki/List_of_micronutrients.
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"Vitamin D 101: A Detailed Beginner’s Guide," Healthline, https://www.healthline.com/nutrition/vitamin-d-101.
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"Vitamin D - The Nutrition Source," Harvard School of Public Health, https://nutritionsource.hsph.harvard.edu/vitamin-d/.
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"Vitamin D and Immunity," National Institutes of Health, https://pubmed.ncbi.nlm.nih.gov/21849106/.
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"Calcium’s Role in Bone Health," American Journal of Clinical Nutrition, https://academic.oup.com/ajcn/article/80/6/1689S/4690513#F3.
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"Vitamin D Supplementation Improves Sleep Quality," PubMed, https://pubmed.ncbi.nlm.nih.gov/35578558/.
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"Vitamin D for Sleep and Cognition," PubMed, https://pubmed.ncbi.nlm.nih.gov/34917293/.
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"Vitamin D and Muscle Health," PubMed, https://pubmed.ncbi.nlm.nih.gov/32857128/.
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"Vitamin D and Cancer Prevention," YouTube, https://www.youtube.com/watch?v=GbSQrp4TN9o.
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