This Might Be the Most Important Vitamin D Study Ever

Vitamin D is what I call the master hormone. It's the central hormone to all other hormones and it's absolutely essential to health. Your body makes vitamin D when the skin gets exposed to UV radiation from the sun. But what if there's no sun? Interestingly, although I live in Estonia, which only gets 60 to 80 days of sunlight per year, I've never seen vitamin D deficiency in my blood work, even without taking vitamin D supplements. There was a recent 2025 study that finally gave an answer to that. In this video, I'm going to share the study and other ways of keeping your vitamin D levels optimal without sunlight. The answer is exercise. This 2025 randomized control trial on obese participants saw that those who exercised maintained their vitamin D levels normal during the winter, whereas those who didn't exercise saw a 15% decrease in their vitamin D. They saw the results even without weight loss. You see, vitamin D gets stored in your body fat. And if you have a lot of body fat, vitamin D gets locked away. That's why obese and overweight individuals have been seen to have a much higher likelihood of vitamin D deficiency compared to normal weight individuals. Losing weight has been seen to increase vitamin D status in both men and women as confirmed by a 2016 meta analysis. You essentially release the vitamin D that's locked up in body fat. In this 2025 study, exercise even without weight loss resulted in better vitamin D status. But if the people didn't lose weight, how did they get access to their vitamin D that was locked in the body fat? Body fat is basically stored triglycerides. Triglycerides are three fatty acid chains with a glycerol backbone and is basically the main form of fat used for fuel and energy storage. Whenever you eat too much food, whether that be too much sugar, too many fries, too much steak, too much eggs, too many potatoes, too much of anything, that surplus of food will be converted into triglycerides. Your body fat isn't made of sugar. Even if you eat too much sugar, it's triglycerides. During weight loss, your body takes the stored triglycerides in your body fat to be used for energy balance. Thus, you lose body fat. During exercise, your body mobilizes triglycerides from your body fat to be used for fuel because exercise increases fat oxidation. At least as long as you're not gulping down Gatorade during the workout. Exercise long enough and even the most insulin resistant and most diabetic person will start burning fat for fuel. The reason they didn't lose weight is because the participants weren't told to eat less food and they probably made up for the energy expenditure during exercise with increased food consumption. If they had lost weight during the study, then their vitamin D status would have probably even increased. But in this particular case, exercise slowed down the decline in vitamin D during the winter. Exercise is also thought to stimulate an enzyme called CYP27B1, which converts vitamin D into its active form, making it more bioavailable. Even a single bout of exercise has been seen to increase blood vitamin D concentrations. So although I live in Estonia and I realistically get only 60 days of sunlight per year, I've never had vitamin D deficiency in my blood work. The reason is that I'm lean which prevents vitamin D from being locked away in my body fat and it's mobilized into my blood during exercise which I do regularly. Exercise mobilizes the vitamin D and also activates it which is the key here. It makes sense evolutionarily as well. During the winter, at least in the northern countries, there wasn't a lot of sunlight, and people tended to lose body fat during the winter. They quote unquote bulk up in the autumn and spring and summer period, and then they lose the body fat because there's less to eat during the winter. And by doing that, they mobilize some of the vitamin D that was stored in their body fat during the summer. It's just that people in the modern world, they don't exercise, they don't lose body fat, and they don't get exposed to enough sunlight to begin with. This doesn't mean that you can just be indoors all day and exercise. You still need normal amounts of sunlight to get adequate vitamin D. At minimum 30 minutes per day is needed. It's just that exercise helps to maintain normal vitamin D levels, especially during the winter. You're also not getting the other benefits of sunlight from exercise, such as infrared light and red light. You do increase nitric oxide with exercise, which improves blood flow and cardiovascular health, but you're missing out on infrared light that increases melatonin and it regulates your sleep, etc. You can also get vitamin D from food, and this does affect blood vitamin D as well. However, it's hard to get the full RDA from food alone. Cod liver oil, trout, salmon, milk, sardines, eggs, and cheese. All right, let me give you some final tips. If you're overweight or obese, lose the weight. It not only improves your vitamin D status, but also improves overall health and longevity. Get adequate vitamin D from sunlight. At least 30 minutes per day to get the RDA. Exercising slows down the loss of vitamin D and mobilizes it from body fat. There are also some supplements that can increase vitamin D utilization like boron. So whenever you take vitamin D supplements, take boron. When taking vitamin D supplements, you should also take vitamin K2 because vitamin D increases calcium in the blood and K2 helps to store the calcium in bones. If you have high vitamin D levels from supplementation, then stop taking it because excessively high vitamin D can be harmful. Sunlight and daylight exposure are critical to your overall health by regulating your circadian rhythms, your mood, and energy. In fact, circadian rhythms are thought to be a new hallmark of aging. Check out my video about it