Welcome to Straight Talk on Health. I’m your host Dr. Chet Zelasko. Straight Talk on Health is a joint production with WGVU in Grand Rapids MI. I examine the practical application of health information. Nutrition. Exercise. Diet. Supplementation. I look at the science behind them and let you know whether it’s something to consider or not. You can check out other things that I do on my website Drchet.com and sign up for my free emails.
The very first audio I ever recorded was about Vitamin D. I thought it was time to present it again 15 years later updated with any significant research. Vitamin D is a nutrient that was hot in 2010 and remains hot right now. Healthcare professionals and physicians are telling people they should be taking more vitamin D. Doctors are recommending that just about everyone get his or her vitamin D levels tested. It can seem a little overwhelming. I’m going to tell you everything you need to know about vitamin D—what it is, what it does in your body, how much you need, how to test for vitamin D, and how much vitamin D may be too much. That should help you make a decision about whether you need to take a vitamin D supplement. So let’s get started.
What Does Vitamin D Do in Your Body? Vitamin D is a fat-soluble vitamin. Simply put, that means you can store it in your fat cells. The chemical structure is very similar to cholesterol and steroid hormones. But similar doesn’t mean it does the same things. Vitamin D is important for calcium absorption in the gut. It also helps maintain calcium and phosphate concentrations in the blood. That’s important for normal bone health, but it’s also important to prevent hypocalcemia tetany. What’s that, you might ask? Muscle cramps—and we all know what those can be like!
If you don’t get enough vitamin D from diet or sunlight, bones can become thin and subject to fracture. Severe vitamin D deficiency can lead to soft bones; it’s called Rickets in children or osteomalacia in adults. In modern countries, that rarely happens anymore, but it’s possible for a person to get enough vitamin D to prevent soft bones but not enough to prevent other bone conditions. The lack of vitamin D and calcium are related to osteoporosis in the elderly. While those are certainly important for a strong skeletal system, vitamin D has other roles in your health.
Vitamin D is important in how your muscular and nervous systems work, it boosts your immune system, and can help reduce inflammation. It has also shown a relationship to CVD. As if that’s not enough, vitamin D is very important in cell reproduction and differentiation. That simply means it helps the new cells decide what type of cells they will become. With all that, you can see that vitamin D is so much more important than just helping keep your bones strong. Recent research has shown exactly what the lack of vitamin D can mean.
Recent research circa 2010. Since the early 1990s, researchers have been tracking where diseases occur in the United States and Canada. They’ve found that people living north of the 35th parallel have higher rates of depression, heart disease, diabetes, cancer, and multiple sclerosis than those living below it. That line runs through Arizona and Georgia. When you look at the map, it’s pretty clear that the further north you live, the higher the rate of cancer. Researchers eliminated every other cause until they came up with the reason: the decrease in exposure to sunlight and lack of vitamin D. In a recently published study, researchers speculated that increased exposure to sunlight or taking supplemental vitamin D could potentially decrease mortality from all cancers in the North by 10%.
Based on the mortality rate from all cancers before 2010 and 2024, the last year that has been analyzed, absolute cancer deaths has increased. However, that’s mostly due to the increase in population. When you look at the rate of cancer mortality, Men have decreased from 215 per 100,000 before 2010 to ~173 per 100,000 by 2019, with continued decline through 2023. For women: ≈147 per 100,000 before 2010 down to ~126 per 100,000 by 2019, also continuing downward. Can we attribute that to increased vitamin D levels? No one has done that research yet. Certainly there are better cancer treatments. Research from the National Health and Nutrition Examination Survey show that serum vitamin D levels have gone up through that time frame but to date, no research has been done to suggest that vitamin D contributed to that decrease. Still, it is an interesting observation.
The best way to determine your vitamin D status is a serum 25-hydroxyvitamin D test. The test gives you an indication of the amount of vitamin D you produce in the skin as well as that obtained from food and supplements. Vitamin D circulates in the blood for up to two weeks after it’s made or ingested. That means the test reflects your intake over the past two weeks, but it doesn’t tell you what’s stored in your tissues. Based on recent research, your vitamin D levels should be greater than 30 ng/mL or ≥75 nmol/L, depending on the units used on your tests. Some researchers feel that levels closer to 60 ng/mL may be even better. Certainly, getting to 30 ng/mL will be good for most people. That hasn’t changed in the past 15 years.
Where do we get vitamin D? The primary source of vitamin D is sun exposure as suggested earlier. Ultraviolet B can penetrate the skin and convert a steroid precursor into previtamin D3, which is then converted to vitamin D3. Here’s something you need to know. You can be exposed to UVB rays on a cloudy day and even sitting in the shade. But if you sit in the sun indoors, you’re out of luck; the UVB doesn’t penetrate glass, so you won’t get a tan or make vitamin D. Also any sunblock with a sun protection factor or SPF of 8 or more will also block the production of vitamin D. We fear skin cancer, as well we should, but we need the vitamin D. What can we do to get vitamin D if we’re not exposed to the sun on a regular basis?
Unless you eat fresh or canned fish on a regular basis, you probably won’t get much vitamin D in the foods you eat. Vitamin D is added to other foods, such as milk and cereals. The calcium in milk is important for bones, and the vitamin D added to milk helps with the absorption of calcium as mentioned earlier. But what if you don’t like fish and you’re lactose intolerant? You’ll have to get your vitamin D from a dietary supplement.
In supplements, vitamin D is available in two forms, D2 (ergocalciferol) and D3 (cholecalciferol). The two forms of vitamin D have both been used to help with Rickets, but recent research suggests that they are metabolized differently. Vitamin D3 could be more than three times as effective as vitamin D2 in raising serum vitamin D and can maintain higher levels for a longer time. If you’re going to take a vitamin D supplement, it should be vitamin D3.
The next logical question is how much vitamin D should you take? The RDA in 2010 was 200 to 400 IU or 5 to 10 mcg per day depending on age. The Institute of Medicine convened a committee to consider recent research and update the RDA for vitamin D in 2010. The new RDA is set at 600 IU or 15 mcg for ages 10-70 and 800 IU or 20 mcg for those older than 70 years. The current Upper Limit was set at 4,000 IU or 100 mcg for all adults.
Can You Overdose On D? While vitamin D isn’t toxic until levels get well into 100,000 IUs per day, we want to improve our bones and immune system, not cause other problems. Based on research, doses of 10,000 IU of vitamin D3 per day for up to five months do not cause toxicity. But be prudent and base your intake on your serum vitamin D level in conjunction with your doctor’s recommendation.
That’s everything you need to know about vitamin D, including the research up through the summer of 2010 and updated in 2026. That’s all the time I have for this episode. If you like this podcast, please hit the share button and tell your friends and colleagues about it. Until next time, this is Dr. Chet Zelasko saying health is a choice. Choose wisely today and every day.
Nutrients. 2024 Oct 9;16(19):3414.
CA Cancer J Clin. 2024 Jan-Feb;74(1):12-49.
