Spotlight On…Vitamin D
- erikasiesennop
- Dec 22, 2025
- 4 min read
Let’s talk about vitamin D! This vitamin is important for many reasons and it’s not uncommon for folks to have low or low-normal levels of vitamin D. There has been a lot more discussion about vitamin D in recent years and, while we know it does several important things, research is still determining the full extent of its role. We’ll take a closer look!
Functions and Ongoing Research of Vitamin D’s Roles
Research is always ongoing and there is a lot of information about vitamin D that hasn’t been confirmed or still needs to be better understood. The below items include well-established information about vitamin D as well as possible roles of vitamin D. There is still a lot to be learned and confirmed!
Bone Health: Helps your body absorb the calcium needed for strong bones. Calcium and vitamin D also work together to help prevent osteoporosis, which weakens bones and leaves them more susceptible to breaking. Vitamin D also helps regulate phosphorus in the body, which is also vital for bone health.
Heart Health: Research is being conducted to determine if vitamin D can play a role in improving heart health, but results so far have been mixed. If it is shown to be helpful, researchers also want to determine if certain levels of vitamin D make the most impact and what those levels are. What is generally known is that vitamin D is important for healthy blood vessels, which supports normal blood pressure.
Gastrointestinal Health: Some research has shown that vitamin D may help with calcium absorption in the gut and seems to play a role in strengthening the intestinal barrier. A strong intestinal barrier helps the gut absorb beneficial nutrients while keeping harmful bacteria out.
Depression: Vitamin D is necessary for proper brain functioning. There is a lot of talk around vitamin D and mental health, and some studies have shown links between low vitamin D and increased risk of depression. There is no conclusive evidence here, and research shows that taking vitamin D supplements do not prevent or reduce symptoms of depression.
Immune support: There is new and promising research about the potential benefits of vitamin D supporting immune function in those with autoimmune disorders.
Required for muscle movement and assists nerves in sending signals between your body and brain.
How much do you need per day?
This varies based on age, although the National Institutes of Health (NIH) recommends 600 IU (international units) per day for adults aged 19-70. Your own needs may vary, so it’s always good to ask your doctor about your vitamin D target. The upper limit for adults 19 years and older is 4000 IU per day, unless otherwise specified by your doctor.
Food Sources
Some fatty fish (such as salmon, trout, sardines) naturally contain vitamin D. Fortified dairy products, fortified plant-based foods, and egg yolks can also be good sources of vitamin D. Check the labels to see if a food has been fortified with vitamin D.
Supplements and Dosing
There is a lot of room for variation with supplementation of vitamin D. It’s best to ask your doctor to check your blood levels to determine if you are deficient and if supplementation would benefit you, as well as how much it’s recommended for you to take, how often, and in what form. Research is seeming to show that higher doses of vitamin D supplementation don’t necessarily offer more benefit over more modest doses, so again it’s good to talk with your doctor about what will work best for you.
Fat Soluble
Vitamin D is fat soluble, meaning it requires fat for absorption and is stored in the body’s fatty tissues and liver. This is why it’s usually recommended to take vitamin D supplements with a meal. Conditions that impair fat absorption, such as Crohn’s or Celiac diseases) can impact vitamin D absorption. Because vitamin D can be stored (unlike water soluble vitamins that are excreted from the body), our bodies can build up a necessary supply. On the other hand, this also means excessive amounts and higher-than-needed supplementation can lead to toxicity. This is rare and mainly occurs from high or excessive supplementation.
Winter vs Summer
This vitamin is important all year round and we especially hear about it in the winter time. In the summer when we’re soaking up the sun our bodies have increased exposure to UV light, which the body needs to create vitamin D. With shorter winter days comes less daylight and more time indoors away from the biting cold (and away from sunshine!). It’s not to say our bodies don’t create any vitamin D in the winter. It's just that, depending on how cold it is and, therefore, how much you have to bundle up, you may get some sun exposure in the winter, but it’s likely less than in the summer time. Exposure to direct sunshine for 15-30 minutes can help your body make a decent amount of the recommended daily vitamin D for adults. Keep in mind that you do want to limit how much time you spend in direct sunlight, though, to reduce risk of skin cancer-causing UV radiation. This is where sunscreen with sun protection factor (SPF) is important if you’ll be in the sun for more than a few minutes. In addition to which season we’re in, other factors that can impact how much vitamin D one’s body can make from sun exposure include: time of day, length of day, cloud cover, smog, melanin content of skin, and others.
Vitamin D is hugely important for our bodies! If you want to learn more, have concerns about your intake or levels of vitamin D, or want to find ways to enhance your vitamin D intake, feel free to reach out! As always, we’re here and ready to help.
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Written by Sarita Aguirre, MS, RDN, LDN, CEDS-C
