Key Takeaways

  1. There is a widespread deficiency of Vitamin D globally, influencing various health conditions.
  2. Specific groups, like pregnant women and older adults, require close monitoring of Vitamin D levels.
  3. Vitamin D can be obtained from sunlight, diet, and supplements, each with recommended dosages.
  4. Low levels of Vitamin D are linked to various health issues, including bone diseases and chronic conditions.

Who can best benefit from Vitamin D level determination?

Nearly one in two (48%) individuals worldwide have vitamin D deficiency (Vitamin D level less than 20 mg/dL, or less than 50 nmol/L) [1], and less than one in four (23%) people worldwide have optimal levels of Vitamin D in their blood (between 30 and 100 mg/dL) [2]. Cardiovascular disease, cancer, stroke, diabetes, dementia and osteoporosis are common chronic diseases worldwide that contribute greatly to illness and death in the population. Each of these debilitating diseases is influenced by Vitamin D levels, and low levels of Vitamin D are a risk factor for developing all of these common and chronic diseases. Moreover, common acute respiratory infections are influenced by Vitamin D levels, and may be prevented by Vitamin D supplementation to adequate levels. Thus, anyone who is interested in improving their general health and avoiding common diseases should monitor their blood levels of Vitamin D.

Pregnant women should pay particular interest to Vitamin D blood levels, since pregnancy health and the health of the newborn are affected by Vitamin D.

Others that are particularly at risk for low Vitamin D levels and should be tested include individuals who:

  • are over age 65
  • are obese
  • just had bariatric surgery (weight loss surgery)
  • have limited exposure to the sun
  • wear long clothing outdoors
  • have dark skin
  • have osteoporosis or thin bones
  • are taking medicines that may lower Vitamin D levels (see list of drugs under “Prescription Medicines” below)
  • have problems with intestinal absorption of vitamins because of an underlying condition such as colitis or celiac disease.

When is the best time to measure Vitamin D levels?

You can measure your Vitamin D levels at any time you wish, since the blood levels of Vitamin D tend to be stable over the course of any 24-hour period.

How can I better understand my Vitamin D level results?

  • Optimal: 30 to 100 ng/dL.
  • Suboptimal: 21 to 29 ng/dL.
  • Deficient: Equal to or less than 20 ng/dL.
  • Too high: Greater than 100 ng/dL.

Deficient levels of Vitamin D can lead to elevated levels of parathyroid hormone (a hormone that regulates bone and calcium metabolism), a condition known as secondary hyperparathyroidism. Secondary hyperparathyroidism can cause bone disease, and it can also cause calcium to build up in tissues and organs such as the heart and blood vessels.

How can I raise my Vitamin D levels?

Dietary and other lifestyle modifications

  • Exposure to daily sunlight for a sufficient length of time (30 minutes per day) is important during the winter time to maintain Vitamin D3 levels, especially for individuals with darker skin tone. Although sunscreen blocks most of the UVB rays that are required for Vitamin D production, it is recommended to wear sunscreen when outdoors for long periods of time (greater than 30 minutes) to prevent skin cancer. Extended outdoor exposure to the sun with sunscreen may allow enough UVB penetration for sufficient production of Vitamin D [3].
  • Vitamin D3 can also be obtained from dietary consumption of various types of fatty fish, including salmon, sardines, tuna, herring, or mackerel, chicken breast, egg yolks, beef liver or fish liver, or food that is artificially supplemented with Vitamin D3, such as milk, almond or soy milk, tofu, cereal, or orange juice.
  • Vitamin D2 can be obtained from the diet by consumption of certain plant fluids, such as mushrooms.

Supplement additions

  • Vitamin D3 supplementation is an easy and efficient method to restore Vitamin D levels to healthy levels.
  • The recommended amount of Vitamin D3 supplementation depends on the age, health status, and medical history of the person taking the supplement:
    • For infants and toddlers less than 1 year of age, the recommended dose is 2000 International Units (IU) of Vitamin D3 per day for six weeks until target blood levels are reached, followed by 400 to 1000 IU per day once blood levels are in range.
    • For children between 1 and 18 years of age, the recommended dose is 2000 IU of Vitamin D3 per day for six weeks until target blood levels are reached, followed by 600 to 1000 IU per day for maintenance.
    • For adults, the recommended dose is 6000 IU of Vitamin D3 per day for eight weeks until target blood levels are reached, followed by 1500 to 2000 IU per day once blood levels are in range.
    • For obese individuals, people with malabsorption diseases, and people taking certain medications, the recommended dose is 6,000 to 10,000 IU/day, until target blood levels are reached, followed by a maintenance dose of 3,000 to 6,000 IU/day to maintain blood levels in the desired range.
    • Vitamin D supplementation may interact with other medications, and individuals taking these other medications should talk to their doctor before taking any Vitamin D supplement: aluminum-containing phosphate binders for kidney disease, atorvastatin (Lipitor) for elevated cholesterol, calcipotriene (Dovonex, Sorilux) for psoriasis, cytochrome P-450 3A4 (CYP3A4) substrates, or digoxin (Lanoxin) for heart disease.
  • Common natural supplements that many people take may decrease Vitamin D levels as a side effect, including St. John’s wort and kava kava. Individuals taking these supplements may require higher levels of Vitamin D supplementation.


  • A recent report that analyzes many other studies concludes that for older adults, combining Vitamin D supplementation with resistance exercise training leads to an additive improvement in musculoskeletal strength, suggesting that exercise and sufficient Vitamin D blood levels are both important for physical strength [4].


  • Smoking has been associated with lower Vitamin D levels, and expectant mothers who smoke have an increased risk of Vitamin D lowering during low-sun exposure months in northern regions [5], suggesting a link between smoking, low Vitamin D levels, and poor maternal health.
  • Passive smoking is also associated with lower Vitamin D level in children [6], suggesting that those who spend time with smokers should carefully monitor their Vitamin D levels.


  • There is little evidence that alcohol intake levels substantially affect Vitamin D levels [7], suggesting that modifying alcohol intake will not dramatically alter Vitamin D levels in the long term.

Prescription Medicines

Drugs that lower Vitamin D levels include:

  • Anti-seizure medications, including phenytoin, phenobarbital and carbamazepine.
  • Certain blood pressure medicines, such as nifedipine and spironolactone.
  • Cancer treatments and chemotherapies, such as taxol.
  • Estrogen-blocking drugs for breast cancer, including tamoxifen and fulvestrant.
  • Drugs for various infections, such as rifampin or isoniazid for tuberculosis, ritonavir for HIV, and clotrimazole for fungal infections.
  • Various steroidal medications, including prednisone, dexamethasone, and methylprednisolone.
  • Drugs that interfere with intestinal absorption of vitamins, including Orlistat (Xenical, Alli) or stimulant laxatives.

Individuals taking any of the above medications may require higher Vitamin D3 supplement doses to restore blood levels to an optimal value.

Where can I learn more?

Health and medical importance of Vitamin D levels

Vitamin D is important to help the body absorb phosphorus and calcium into the bloodstream, and these elements are essential for bone growth. Thus, Vitamin D is important for bone metabolism, and low Vitamin D levels can lead to bone diseases including osteoporosis [8]. Osteoporosis is a disease that causes bones to be weak or brittle, and can lead to bone fractures, falls and injury. Osteoporosis is very common in most countries, particularly among post menopausal women, with a worldwide prevalence of 1 in 5 [9]. Patients with osteoporosis frequently have mildly lower levels of Vitamin D.

Recent evidence suggests that Vitamin D is important for many other body functions, and that Vitamin D has substantial effects on many different organs in the body. For example, individuals with low circulating levels of Vitamin D are more prone to suffer from acute respiratory infections. Furthermore, it has been shown from many studies that increasing blood levels of Vitamin D to suitable levels can diminish the risk for these acute respiratory infections [10]. Moreover, low Vitamin D blood levels are associated with worsening of asthma, and supplementation with Vitamin D to restore suitable blood levels prevents these complications of asthma as well [11].

In addition, low Vitamin D blood levels have been associated with other serious diseases, including multiple types of cancer such as colon, breast, and prostate cancer [12]. Supplementation with Vitamin D to achieve sufficient blood levels has been shown to decrease the overall death from cancer, according to a recent analysis, although Vitamin D supplementation does not decrease the incidence (occurrence) of cancer [13]. Importantly, low levels of Vitamin D have been associated with the development of cognitive impairment (brain decline) and Alzheimer’s disease [14], and there is recent evidence that supplementation with Vitamin D may prevent cognitive decline in healthy Black adults [15].

Low Vitamin D levels are also correlated with the development of Type II, or adult onset diabetes [16]. Whether supplementation of Vitamin D can reverse Type II diabetes is controversial, but there is evidence that supplementation with high levels of Vitamin D for short periods of time can be used to effectively treat some aspects of this disease for some groups of patients [17].

Moreover, low levels of Vitamin D are associated with inflammatory bowel disease, including Chron’s disease and ulcerative colitis, and supplementation with Vitamin D has been show to reduce the incidence of these d[18] In addition, a recent review concludes that supplementation with Vitamin D to achieve desired blood levels is associated with reduction of symptoms of several other diseases, including relief from major depression, pain from fibromyalgia (a disorder characterized by widespread body pain and fatigue), and the symptoms of atopic dermatitis (a condition characterized by itchy, dry, and inflamed skin) [19].

Pregnant women who are deficient in Vitamin D have an increased risk for medical complications during their pregnancy, including preeclampsia (high blood pressure during pregnancy) and the need for cesarean section [20]. In addition, the children born from mothers with low Vitamin D levels may suffer from asthma or dental cavities.

However, blood levels of Vitamin D that are too high can cause health problems as well, including too much calcium in the blood (hypercalcemia) and kidney damage. These changes can lead to nausea, vomiting, and muscle weakness [21]. Thus, it is important to regularly monitor one’s Vitamin D blood levels to make sure that they are neither too high nor too low.

What forms of Vitamin D should be measured for health monitoring?

There are several different forms of Vitamin D in the human body, including Vitamin D3 and Vitamin D2 [22]. Almost all (about 90%) of Vitamin D3 in the body is obtained from sunlight ultraviolet B (UVB) rays on the skin, which converts 7-dehydrocholesterol (a normal molecule in the skin) to Vitamin D3 [23]. A small amount (about 10%) of Vitamin D3 in the body is obtained from dietary consumption of fish or eggs, or food that is artificially supplemented with Vitamin D3, or supplements that contain Vitamin D3. Vitamin D2 is a different form of Vitamin D that can obtained from the diet by consumption of certain plant fluids, such as mushrooms, or supplements than contain Vitamin D2.

Once Vitamin D3 or D2 is in the bloodstream, the liver converts Vitamin D3 or D2 to a different form of the vitamin, called 25-hydroxyvitamin D3 or D2 (we will refer to either of these Vitamin D forms here as “25OH Vitamin D”). 25OH Vitamin D lasts for a long time in the blood stream, with a half-life of two to three weeks, meaning that after two to three weeks, the amount of 25OH Vitamin D in the blood is one-half of the original value, assuming no new sources for accumulation. For this reason, 25OH Vitamin D is the best measure of total storage levels of Vitamin D in the body. Thus, 25OH Vitamin D is the preferred form of Vitamin D for doctors and medical scientists to measure for human health and disease, since blood levels of 25OH Vitamin D correlate best with the health-related effects of this vitamin. Hence, the 25OH Vitamin D blood level is measured by SiPhox as a marker for Vitamin D status.

25OH Vitamin D is further converted by the kidney and other tissues to a different form of Vitamin D, called 1,25 (OH)2 Vitamin D, which is the biologically active form of Vitamin D. However, since 1,25 (OH)2 Vitamin D is rapidly converted to other forms of the Vitamin (i.e. rapidly metabolized), 1,25 (OH)2 Vitamin D does not accurately reflect body storage levels of Vitamin D. Therefore, blood levels of 1,25 (OH)2 Vitamin D do not correlate well with the health-related effects of this vitamin, and SiPhox does not measure 1,25 (OH)2 Vitamin D.

Tracking your Vitamin D with SiPhox Health:

  • At-home kit delivered to your home
  • Fingerprick sample self-collection (low-pain, adjustable lancets)
  • $295 one-time or subscribe to get $85 per test*
  • Number of biomarkers included: 17 (4 inflammation markers including Vitamin D)
  • Sleep and activity tracking: Included, 200 devices supported
  • 2-5 business days after collection

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Disclaimer: If you have any medical questions or concerns, please talk to your healthcare provider. The articles on the SiPhox Health Hub are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis or treatment.