After vitamin D is absorbed through the skin or acquired from diet or supplements, it is stored in the body’s fat cells, remaining inactive until it’s needed. Through a process known as hydroxylation, the liver and kidneys convert this stored vitamin D into its active form, calcitriol, which the body can use. It’s worth noting that whether you obtain vitamin D2 or D3, and whether it’s from sunlight or nutritional sources, the body efficiently utilizes each type. “The body can use each perfectly fine,” explains Dr. Karl Insogna, director of Yale Medicine’s Bone Center.
These are the fundamental facts about vitamin D. However, many people still have important questions: Where do you get vitamin D effectively? How much vitamin D should you aim for daily? And when should concerns about vitamin D levels arise?
To address these common points of confusion, we consulted with Yale Medicine doctors to clarify the facts about vitamin D and dispel some prevalent myths.
Below are their expert insights, edited for clarity and conciseness.
Dispelling Vitamin D Myths and Highlighting Key Facts
Myth: The more vitamin D you consume, the better it is for your health. Fact: Absolutely not.
— Thomas Carpenter, MD, Yale Medicine pediatric endocrinologist and director of the Yale School of Medicine’s Center for X-Linked Hypophosphatemia
This is a common misconception. Vitamin D is fat-soluble and stored in your body’s fat tissues. If you are smaller in stature and consume high doses of vitamin D, you may have less fat storage available. This can lead to excess vitamin D circulating in your blood, potentially causing you to absorb too much calcium and creating a toxic situation known as hypercalcemia. It’s also not precisely known how long it takes to exceed safe upper limits of vitamin D intake before it becomes harmful. While modest increases above the Recommended Daily Allowance (RDA) are generally not dangerous, excessive amounts can be.
Recently, Dr. Carpenter treated an infant who presented with alarmingly high vitamin D blood levels, reaching into the hundreds when the normal range should be between 20 and 50 nanograms per milliliter (ng/mL). This child developed hypercalcemia, requiring hospitalization and treatment with multiple medications to bring calcium levels back to a safe range.
High-dose vitamin D supplements, such as 50,000 IU tablets, are now available over the counter. While such high doses might be prescribed for specific medical conditions under strict medical supervision, for most individuals, this amount is far too much and can dangerously elevate vitamin D levels.
When choosing vitamin D supplements, always aim for products that provide the RDA appropriate for your age group. For most healthy adults, this is 600 IU daily, increasing to 800 IU for those over 70, who may synthesize vitamin D and absorb calcium less efficiently, especially in women post-menopause. Infants require smaller amounts, between 200 and 400 IU in their first year.
Myth: Everyone should routinely have their vitamin D levels checked. Fact: Generally, no.
— Karl Insogna, MD, director of Yale Medicine’s Bone Center
For most healthy individuals, routine vitamin D testing is unnecessary. Testing is primarily recommended for specific populations at higher risk of deficiency. These include individuals who are institutionalized, patients with gastrointestinal disorders like inflammatory bowel disease or osteoporosis, those who have undergone weight loss surgery, individuals on anti-convulsant medications, and children who are immobilized or have limited outdoor activity. Dr. Insogna recommends that individuals over the age of 70 should have their vitamin D levels checked at least once.
Additionally, people whose cultural or religious practices necessitate full body covering, especially in northern regions with less sunlight, and those with diets low in vitamin D-fortified foods like dairy, may also be at risk of vitamin D deficiency and should consider getting tested.
Myth: Vitamin D deficiency is a widespread epidemic. Fact: No, it’s not.
— Thomas Carpenter, MD, Yale Medicine pediatric endocrinologist and director of the Yale School of Medicine’s Center for X-Linked Hypophosphatemia
According to data from the USDA and National Health and Nutrition Surveys, using 20ng/mL as the threshold for deficiency, the majority of the population is not vitamin D-deficient. Vitamin D deficiency is more commonly observed in specific groups, particularly breastfed infants, especially during winter months. Breast milk is naturally low in vitamin D. This is why the American Academy of Pediatrics recommends vitamin D supplementation for all breastfed infants. If infants are given liquid multivitamin drops, they are likely receiving sufficient vitamin D. However, if not, they should be given 200 IU of vitamin D daily for the first two months, increasing to 400 IU daily thereafter until they are consuming formula or milk, both of which are fortified with vitamin D.
Myth: The best way to get vitamin D is from sun exposure. Fact: Definitely not.
— David J. Leffell, MD, Yale Medicine dermatologist and chief of Dermatologic Surgery
Dermatologists and skin cancer prevention experts are concerned about misinformation regarding vitamin D and sun exposure.
Claims suggesting that daily sun exposure is necessary to produce sufficient vitamin D for health are simply untrue. Most people can adequately obtain their vitamin D through nutritional supplements and vitamin D-fortified foods.
Some individuals, often not experts in dermatology or skin cancer biology, advocate for tanning to boost vitamin D levels. However, it’s a well-established fact that UVB radiation from the sun is a primary cause of skin cancer. Protecting your skin from excessive sun exposure is crucial. As a physician treating melanoma patients, Dr. Leffell strongly advises the public that using tanning beds or intentionally tanning for vitamin D production is never justified. Opt for a vitamin D supplement instead to ensure you get where do you get vitamin d safely and effectively.
