The “D”eal with Vitamin D? Benefits, Deficiency & Dosage
Updated: 5 days ago
Original posting 12/13/2019, Updated: 10/20/2026
Vitamin D advantages, vitamin D deficiency, optimum vitamin D levels, and how much vitamin D you need
We usually call vitamin D the "sunshine vitamin" as we have the ability to synthesize it using ultraviolet B (UVB) rays from sunlight, however, there is more to vitamin D than that! For example, vitamin D is crucial for bone mineralization, calcium absorption, muscle strength and function, and immunity, as well as being present in various other pathways involving inflammation, cell proliferation, metabolism, and immune system regulation.
And here's yet another interesting thing about vitamin D:
Vitamin D does not fit the description of a regular vitamin as it acts as a precursor for hormones.
Why is vitamin D so important?
The best-known action of vitamin D is calcium and phosphorus homeostasis and bone health.
Sufficient vitamin D helps in calcium absorption and proper bone mineralization; extreme deficiency may lead to adult osteomalacia and rickets in children.
However, vitamin D is involved in numerous actions including:
Bone and skeletal health
Muscle activity
Calcium and phosphorus metabolism
Regulation of the immune system
Cellular proliferation and differentiation
Inflammatory pathways
Glucose metabolism
But it doesn’t mean that vitamin D supplementation will help in prevention and treatment of every condition related to the action of vitamin D in the body. This is one of the major lessons we’ve learned from recent clinical studies. There is a distinction between vitamin D being biologically involved in the disease process, vitamin D deficiency being linked to some diseases, and vitamin D supplementation being a means of prevention and treatment of such diseases. These things may differ a lot.
Risk factors for vitamin D deficiency:
Vitamin D deficiency is widespread throughout the world, although its incidence rate varies according to how vitamin D deficiency is determined, population type, season, location, age, skin color, dietary habits, and many other variables.
There are some individuals who tend to have lower levels of vitamin D. These include individuals who:
Are exposed to less sunlight
Reside in higher latitude regions
Spend most of their time inside homes
Always cover themselves
Have dark skin coloration
Have problems with fat absorption
Undergone gastric surgery
Have obesity
Have low dietary intake of vitamin D
Take medications that interfere with vitamin D metabolism
What about life in the Pacific Northwest?
Being here in Portland and all across the Pacific Northwest, it is possible that sun exposure at different times of the year may make it harder to maintain vitamin D levels, especially in fall and winter months. The body needs UVB light for vitamin D synthesis, and the availability of UVB light on Earth changes significantly depending on latitude, season, time of day, weather conditions, and more. It does not mean that everybody in Oregon and Washington State is deficient in vitamin D, but it is important to take into account these factors.
There is no need to try to burn yourself under the sun to synthesize vitamin D. Sunburning increases risks of skin cancer, and, therefore, vitamin D cannot be an excuse for skipping protection from sunburns.
What does the scientific literature say about vitamin D?
The number of scientific studies that have been published on vitamin D is tremendous over the last few decades. Among some of the most fascinating ones include immune system function, metabolic function, pregnancy, autoimmunity, cancer, cognitive function, and musculoskeletal health. However, the recent advances have also allowed researchers to distinguish what vitamin D can do biologically and what its supplementation has been shown to achieve.
Interesting Fact that drives our providers crazy: Did you know, even though vitamin D is essential to our health in numerous ways, confirmed with quality studies and literature, some insurance companies only pay for vitamin D testing if the patient has diagnosed kidney disease or osteoporosis?
We're looking at you, Blue Cross...
Vitamin D and immunity
Vitamin D receptors are found in many different immune cells, and vitamin D metabolites play a role in both innate and adaptive immunity responses. This has sparked great interest in the use of vitamin D to help maintain immunity. However, studies conducted in humans have yielded mixed results.
According to a 2025 systematic review and meta-analysis of 43 randomized controlled trials, which included more than 61,000 people, there was no significant decrease in the risk of acute respiratory infections in those receiving vitamin D supplements compared to placebo or control group. Studies conducted previously had shown that there is a modest benefit from taking vitamin D, especially when taken daily, but now it's hard to claim that vitamin D supplements help prevent colds and respiratory infections in all cases.
This doesn't mean that vitamin D is irrelevant to immunity. It means that correction of deficiency is a different thing from using high-dose vitamin D to prevent infections.
Vitamin D and autoimmune diseases
There is a link between vitamin D and the immune system and, as a result, vitamin D levels have been heavily researched in the context of autoimmune diseases including multiple sclerosis, rheumatoid arthritis, psoriasis, lupus, and type 1 diabetes. The relationship between low levels of vitamin D and autoimmune diseases is often observed in observational studies.
Clinical trials, on the other hand, are a little trickier to interpret. It seems that supplementation of vitamin D can improve levels of vitamin D and perhaps some inflammatory biomarkers in certain autoimmune populations but there is no solid evidence that vitamin D supplementation alters the natural course of autoimmune disease.
In other words:
Vitamin D is an integral part of general nutrition support, however, it should never be considered a stand-alone therapy for autoimmune diseases.
Vitamin D and Type 2 Diabetes
The research on vitamin D is extensive when it comes to the topics of insulin resistance, prediabetes, and type 2 diabetes. According to a meta-analysis conducted in 2024 that included 11 randomized controlled studies with more than 5,000 participants suffering from prediabetes, supplementation of vitamin D contributed to a 10% decrease in the development of type 2 diabetes, together with an increase in the chance of recovery of glucose regulation. It is good news; however, vitamin D cannot replace healthy nutrition, physical activity, proper sleep, weight management, or any other interventions that are proven to be effective for improving metabolic conditions.
Intriguingly, supplementation of vitamin D seems to have greater influence on glucose regulation among people with type 2 diabetes who lack vitamin D than those who have sufficient levels of vitamin D.
Vitamin D and Cancer
Here's another place where we need to add some critical information to the original vitamin D dialogue. Biologically, there are strong reasons to consider the link between vitamin D and cancer, and multiple observational studies have consistently established such associations. Yet, no evidence exists that vitamin D can prevent cancer from occurring.
Meta-analyses and randomized controlled trials have generally demonstrated that there was little or no effect on cancer development. A possibility of lowering cancer deaths was also reported in some studies, but this is still an investigational topic, rather than an indication to use large doses of vitamin D to prevent cancer. For instance, the meta-analysis of multiple randomized clinical trials did not reveal any association between vitamin D use and reduced incidence of cancer but did report that total cancer mortality was lowered. More recent data from large clinical trials confirm a mixed pattern.
It's quite acceptable to maintain adequate levels of vitamin D for overall well-being, but it is not appropriate to market vitamin D as a cancer prevention or cancer treatment supplement.
Vitamin D and cardiovascular health
Vitamin D deficiency has been found to be linked to several cardiometabolic disorders, such as hypertension, obesity, insulin resistance, and cardiovascular diseases. It does not mean, however, that the vitamin D supplements can help prevent cardiovascular diseases. As per a meta-analysis published in 2024 in randomized controlled trials, vitamin D supplements were ineffective in significantly lowering the risk of major adverse cardiovascular events, myocardial infarction, heart failure, cardiovascular mortality, or overall mortality.
Thus, vitamin D, which has biological significance in cardiovascular physiology, does not help prevent cardiovascular diseases when taken in high doses.
Vitamin D and cognition
There are vitamin D receptors in the brain, and the effects of vitamin D on cognitive aging, Alzheimer’s disease, dementia, and neuroinflammation have been studied. Some observational studies have shown an association between low vitamin D levels and cognitive dysfunction and/or dementia. A 2024 systematic review and meta-analysis of prospective studies did find an association between vitamin D levels and cognitive function. But it does not mean that vitamin D supplementation can prevent Alzheimer’s disease and dementia. Randomized trials of vitamin D and cognition have had mixed results as well.
It is one more area where there is enough evidence for further research but not enough to claim something definitive about treatment.
Vitamin D and Chronic Pain
Vitamin D deficiency may lead to bone pain and muscle weakness, especially if the deficiency is significant. Vitamin D has thus garnered much interest as a possible solution for chronic musculoskeletal pain. However, the research is a bit more complex than what most people know. According to a 2024 systematic review, there seemed to be an inverse association between vitamin D levels and pain severity in some individuals, but the findings were found heterogeneous and inconclusive about a causal link between them.
In other words, if a person has significant vitamin D deficiency and musculoskeletal pain, then treating that deficiency makes sense. However, vitamin D deficiency cannot be automatically assumed to be the cause of chronic pain.
How much vitamin D should you have?
This is where things have changed a lot recently.
The first and main blood test used to measure your vitamin D status is the serum 25-hydroxyvitamin D [25(OH)D]. In the past, many doctors and functional medicine practitioners have set very strict target ranges of 30-50 ng/mL, 40-60 ng/mL or even 50-80+ ng/mL.
However, the 2024 Endocrine Society Clinical Practice Guideline found that there isn't enough scientific data to prove that there is a specific 25(OH)D blood level that will protect you from diseases as an adult. It is a critical point to keep in mind. This does not mean that your vitamin D levels do not matter at all. It means that we need to be more cautious in declaring that everybody needs to get some arbitrary high serum vitamin D concentration for preventing chronic diseases.
What is the amount of vitamin D you should have?
The current RDA for U.S. citizens is:
Infants aged 0–12 months: 400 IU/day
Children aged 1–18 years: 600 IU/day
Adults aged 19–70 years: 600 IU/day
Adults aged over 70: 800 IU/day
Pregnant and lactating women: 600 IU/day
Note that these values are meant to be taken into account by people in general and are not always the exact same values needed in case of vitamin D deficiency. The tolerable upper intake level for adults, including pregnant and lactating women, is 4,000 IU/day, we often recommend doses much higher than the RDA as we adjust based on the serum vitamin D levels every 3-6 months.
And what about vitamin D during pregnancy?
Vitamin D is especially essential during pregnancy due to its influence on calcium homeostasis in mother and bone formation in the fetus. The 2024 Endocrine Society guideline recommends vitamin D supplementation during pregnancy as it is shown by clinical trials that vitamin D could potentially decrease risks of such conditions as preeclampsia, preterm delivery, small-for-gestational-age birth, and neonatal mortality. It is worth noting that the guideline does not recommend routine monitoring of vitamin D level during pregnancy in healthy pregnant women since a certain level of 25(OH)D is required for achieving better results of pregnancy. Your prenatal multivitamin will contain vitamin D, and additional supplementation might be necessary based on your diet, risk factors, and supplementation status. Also, you should not begin taking vitamin D in high doses during pregnancy.
What Is the Difference Between Vitamin D3 and Vitamin D2?
There are two forms of vitamin D supplements:
Vitamin D2 (ergocalciferol)
Vitamin D3 (cholecalciferol)
Both forms increase vitamin D levels in the body. Nonetheless, scientific studies have proven that vitamin D3 increases 25(OH)D better than vitamin D2 when taken regularly.
According to a 2024 systematic review and meta-analysis of randomized controlled trials, D3 increased 25(OH)D levels better than D2, although the effectiveness depends on the dose, frequency of intake, vitamin D levels in the body, and BMI. Therefore, for people opting to take vitamin D orally as a supplement, vitamin D3 will be a better option.
Should you supplement your vitamin D intake with vitamin K2?
It is clear that vitamin K plays an essential role in bone metabolism. Vitamin K-dependent proteins, including osteocalcin and matrix Gla protein, play a role in bone and vascular physiology. Nevertheless, there isn’t enough evidence to say "all vitamin D should come with vitamin K2". We generally recommend taking vitamin D to prevent arterial or renal calcium deposition. There have been some studies that showed that vitamin K supplementation can affect the process of vascular calcification, and of course support bone and teeth remineralization, however, there is much yet to study. Instead of combining each vitamin D preparation with high doses of K2, it is better to take into account the whole picture of an individual’s nutrition, health condition, and other factors. There are times we want to avoid excess vitamin K supplementation, including if someone is taking a medication that can be affected by vitamin K, such as warfarin, to prevent blood clots.
Can one take too much vitamin D?
Of course. Vitamin D is a fat-soluble vitamin; therefore, prolonged excessive supplementation will lead to vitamin D toxicity and hypercalcemia, which is the accumulation of high levels of calcium in blood plasma.
The signs of excess vitamin D are:
Nausea and vomiting
Loss of appetite
Increased thirst
Increased urination
Fatigue
Dizziness
Formation of kidney stones
Damage to the kidneys
The tolerable upper intake level of vitamin D in adults is 4,000 IU/day, but this number could be exceeded temporarily in the case of therapy of established deficiency. That's why I don't advise taking 5,000-10,000 IU of vitamin D daily without any particular reason.
Well then…what is the "D"eal?
Vitamin D is important. Very important. However, the current vitamin D story is not about pinpointing a single perfect serum level and taking increasing amounts of it, but rather about determining who is truly at risk and correcting any deficiencies through an individualized approach.
Here are just a few ways vitamin D is critical for your health:
Bone health
Muscle function
Calcium metabolism
Immune regulation
Cellular signaling
Metabolic health
Studies are still being done regarding vitamin D's effects on autoimmune disease, diabetes, cancer, cardiovascular disease, cognitive function, pregnancy outcomes, respiratory infection, and chronic pain. Some of these areas are quite promising. Some are not so much now that more randomized controlled trials have been completed. This is a good thing. With increased knowledge comes improved recommendations.
If you live in the Pacific Northwest like I do, fall is the ideal time to consider your vitamin D needs.
Vitamin D -- you neeD it!
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Frequently Asked Questions About Vitamin D
What are the benefits of vitamin D?
Vitamin D plays an essential role in bone health, calcium absorption, muscle function, immune system regulation, and metabolism. It also supports normal cellular signaling and helps maintain healthy phosphorus levels in the body.
What are the symptoms of vitamin D deficiency?
Common signs of vitamin D deficiency may include fatigue, muscle weakness, bone pain, frequent illness, low mood, and reduced physical performance. Severe deficiency can contribute to osteomalacia in adults and rickets in children.
How do I know if I have low vitamin D levels?
The most common way to assess vitamin D status is through a blood test called serum 25-hydroxyvitamin D [25(OH)D]. Your healthcare provider can determine whether testing is appropriate based on your symptoms, risk factors, and medical history.
Who is most at risk for vitamin D deficiency?
People at higher risk include those who:
Live in northern climates such as Oregon and Washington
Spend little time outdoors
Have darker skin tones
Cover most of their skin when outside
Have obesity
Have digestive disorders that affect fat absorption
Have undergone gastric surgery
Take medications that interfere with vitamin D metabolism
Do people in the Pacific Northwest need vitamin D supplements?
Not everyone in the Pacific Northwest is vitamin D deficient, but reduced sunlight exposure during fall and winter may increase the risk of low vitamin D levels. Individual needs vary and should be based on risk factors, diet, symptoms, and testing when appropriate.
What is the difference between vitamin D2 and vitamin D3?
Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) can both raise vitamin D levels. However, research suggests that vitamin D3 is generally more effective at increasing and maintaining blood levels of vitamin D over time.
How much vitamin D should adults take each day?
The current Recommended Dietary Allowance (RDA) for most adults ages 19-70 is 600 IU per day. Adults over age 70 are recommended to consume 800 IU daily. Individual needs may differ, especially when correcting a documented deficiency.
Can vitamin D help boost the immune system?
Vitamin D plays an important role in immune function, but current research does not support using high-dose vitamin D supplements to prevent all colds, flu, or respiratory infections. Correcting a deficiency is different from using vitamin D as an infection-prevention strategy.
Does vitamin D help with autoimmune disease?
Low vitamin D levels are commonly observed in people with autoimmune conditions such as rheumatoid arthritis, lupus, psoriasis, and multiple sclerosis. While maintaining adequate vitamin D is important for overall health, it should not be considered a stand-alone treatment for autoimmune diseases.
Is vitamin D good for bone health?
Yes. One of the most well-established benefits of vitamin D is supporting calcium absorption and healthy bone mineralization. Maintaining adequate vitamin D levels helps support strong bones and reduces the risk of deficiency-related bone disorders.
Should I take vitamin D with vitamin K2?
Vitamin K2 may support bone and vascular health, but current evidence does not show that every person taking vitamin D must also take vitamin K2. The decision should be individualized based on health history, medications, and nutritional status.
Can you take too much vitamin D?
Yes. Excessive vitamin D intake can lead to vitamin D toxicity and high calcium levels in the blood (hypercalcemia). Symptoms may include nausea, vomiting, increased thirst, frequent urination, kidney stones, and kidney damage. Unless directed by a healthcare provider, long-term high-dose supplementation is generally not recommended.
Should I get my vitamin D levels tested?
Vitamin D testing may be appropriate for people with symptoms of deficiency, osteoporosis, certain digestive disorders, risk factors for low vitamin D, or other medical concerns. Your healthcare provider can help determine whether testing is warranted.
What is considered an optimal vitamin D level?
Current research suggests there is no universally agreed-upon "perfect" vitamin D level for preventing chronic disease in all adults. The goal is to identify and correct deficiency while avoiding unnecessary high-dose supplementation.
References
Demay MB, Pittas AG, Bikle DD, Diab DL, Kiely ME, Lazaretti-Castro M, Lips P, Mitchell DM, Murad MH, Powers S, Rao SD, Scragg R, Tayek JA, Valent AM, Walsh JME, McCartney CR. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024;109(8):1907-1947. doi:10.1210/clinem/dgae290.
National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. National Institutes of Health. Updated regularly.
Jolliffe DA, Camargo CA Jr, Sluyter JD, Aglipay M, Aloia JF, Ganmaa D, Bergman P, Bischoff-Ferrari HA, Borzutzky A, Damsgaard CT, Dubnov-Raz G, Esposito S, Gilham C, Ginde AA, Golan-Tripto I, Goodall EC, Grant CC, Griffiths CJ, Hibbs AM, Janssens W, Khadilkar AV, Laaksi I, Lee MT, Loeb M, Maguire JL, Majak P, Mauger DT, Manaseki-Holland S, Murdoch DR, Nakashima A, Neale RE, Pham H, Rake C, Rees JR, Rosendahl J, Scragg R, Shah D, Shimizu Y, Simpson-Yap S, Trilok-Kumar G, Urashima M, Martineau AR. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes Endocrinol. 2025;13(4):307-320. doi:10.1016/S2213-8587(24)00348-6.
Kuznia S, Zhu A, Akutsu T, et al. Efficacy of vitamin D3 supplementation on cancer mortality: systematic review and individual patient data meta-analysis of randomised controlled trials. Ageing Res Rev. 2023;87:101923. doi:10.1016/j.arr.2023.101923.
Keum N, Lee DH, Greenwood DC, et al. Vitamin D supplementation for the prevention of total cancer incidence and mortality: an updated systematic review and meta-analysis. Heliyon. 2022;8(11):e11290. doi:10.1016/j.heliyon.2022.e11290.
Mirza MAW, Almansouri NE, Muslim MF, Basheer T, Uppalapati SV, Lakra S, Fatima H, Adhnon A, Filho IW, Mahmood R, Kumar M, Kandel K, Ayyan M. Effect of vitamin D supplementation on cardiovascular outcomes: an updated meta-analysis of RCTs. Medicine (Baltimore). 2024;103(46):e40419. doi:10.1097/MS9.0000000000002458.
Pittas AG, Kawahara T, Jorde R, Dawson-Hughes B, Vickery EM, Angellotti E, Nelson J, Trikalinos TA, Balk EM. Vitamin D and Risk for Type 2 Diabetes in People With Prediabetes: A Systematic Review and Meta-analysis of Individual Participant Data From 3 Randomized Clinical Trials. Ann Intern Med. 2023;176(3):355-363. doi:10.7326/M22-3018.
Tripkovic L, Lambert H, Hart K, Smith CP, Bucca G, Penson S, Chope G, Hyppönen E, Berry J, Vieth R, Lanham-New S. Comparison of vitamin D2 and vitamin D3 supplementation on serum 25-hydroxyvitamin D concentration: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357-1364. doi:10.3945/ajcn.111.031070.
Mattumpuram J, Maniya MT, Faruqui SK, Ahmed A, Jaiswal V, Harshakumar SP. Cardiovascular and Cerebrovascular Outcomes With Vitamin D Supplementation: A Systematic Review and Meta-Analysis. Curr Probl Cardiol. 2024;49(1 Pt C):102119. doi:10.1016/j.cpcardiol.2023.102119.
Jolliffe DA, Brustad N, Chawes B, Cooper C, D'Angelo S, Harvey NC, Litonjua AA, Moon R, Morris SK, Sluyter JD, Weiss ST, Martineau AR. Association between maternal vitamin D supplementation during pregnancy and the risk of acute respiratory infections in offspring: a systematic review and meta-analysis. EClinicalMedicine. 2025;90:103682. doi:10.1016/j.eclinm.2025.103682.
Lau D. In prediabetes, oral vitamin D reduces progression to new-onset diabetes. Ann Intern Med. 2023;176(5):JC55. doi:10.7326/J23-0030.
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