The marker for vitamin D status is 25-hydroxyvitamin-D [25(OH)D], a metabolite of vitamin D3. A 25(OH)D level determines whether a person is deficient, sufficient, or toxic in vitamin D. At this time, there is not a consensus in medicine in what blood levels define these categories.
The Vitamin D Council recommends maintaining serum levels of 50 ng/ml (equivalent to 125 nmol/L*), with the following reference ranges:
- Deficient: 0-40 ng/ml (0-100 nmol/l)
- Sufficient: 40-80 ng/ml (100-200 nmol/l)
- High Normal: 80-100 ng/ml (200-250 nmol/l)
- Undesirable: > 100 ng/ml (> 250 nmol/l)
- Toxic: > 150 ng/ml (> 375 nmol/l)
(*Note: 25(OH)D levels can also be defined in units of nmol/L. The conversion between the two is [nmol/L]=2.5*[ng/ml])
The Vitamin D Council makes a recommendation of 50 ng/ml and defines the above reference ranges for the following reasons:
- The human genome was selected with abundance of vitamin D. Humans evolved in the sun near the equator, synthesizing robust quantities of vitamin D in the skin. Research has shown that lifeguards, farmers near the equator, and sun dwelling hunter gatherers maintain blood levels between 40-80 ng/ml on sun exposure alone1,2,3.
- The Vitamin D Council believes that the maternal 25(OH)D status necessary to provide antirachitic activity for offspring should be considered a biomarker for optimal vitamin D status in humans. Research shows that antirachitic activity in breast milk occurs at 45 ng/ml or higher, but not at 38.4 ng/ml or lower4.
- Research has generally shown that parathyroid hormone is maximally suppressed at 40 ng/ml or higher, another finding that the Vitamin D Council considers a biomarker for optimal vitamin D status5,3.
- The human body is usually unable to achieve 25(OH)D levels above 100 ng/ml on UVB exposure alone3. There are no studies to date to suggest that 25(OH)D levels over 100 ng/ml are beneficial, so the Vitamin D Council believes that the upper limit should be set at 100 ng/ml.
- Vitamin D toxicity manifests itself by hypercalcuria and hypercalcemia. Research has shown that serum calcium levels are not related to 25(OH)D levels up to 257 ng/ml6, but cases of toxicity have been reported at levels as low as 194 ng/ml7. The Vitamin D Council believes that a conservative threshold of 150 ng/ml should be considered the lower limit of toxicity.
The Vitamin D Council recognizes that there are not enough controlled trials at this time to either support these recommendation or oppose these recommendations.
Sun and UVB Exposure
Exposure to sunlight (UVB light) triggers synthesis of vitamin D in the skin, producing up to 10,000 to 25,000 IUs of vitamin D in one erythemal dose of UVB radiation8. The Vitamin D Council considers this the preferable and choice method in elevating and maintaining blood levels since it is the natural and traditional method for humans. More specifically, the Vitamin D Council makes the following recommendations:
- Regular and sensible sun exposure is a healthy practice. Significant vitamin D production occurs when your shadow is shorter than you are.
- When sunbathing, the Vitamin D Council recommends exposing your skin for half the time it takes for it to turn pink. There is no extended vitamin D benefit in extra exposure. In fact, UV light will begin to destroy vitamin D in the skin when the skin is overexposed.
- Overexposure is unnecessary and dangerous. Excessive exposure to sunlight and sunburning will increase risk of squamous and basal cell carcinoma, which over 1,200 people die from per year9. However, the Vitamin D Council believes that sensible sun exposure and maintaining sufficient 25(OH)D levels outweigh the risks.
- If the intention in sunbathing is to produce vitamin D, the Vitamin D Council does not recommend sunblock creams as they will inhibit the skin’s ability to absorb UVB radiation9.
- Tanning beds with low pressure lamps are a suitable substitute to sun exposure as long as the same sensibility is applied to their use.
- Consistent sun exposure in the 21st cenury is not easily achieved. The Vitamin D Council believes that if year round and consistent sun exposure is not possible, then additional measures must be taken, including supplementation and use of low pressure tanning beds.
The Vitamin D Council would like to further note:
- At latitudes of 35 degrees or higher, little if any vitamin D is synthesized during the winter9.
- Darker skin types require longer exposure than light skin types to produce robust quantities of vitamin D. Due to increased melanin, a black person, for example, requires up to 6 times the exposure a white person does to produce the same adequate amounts of vitamin D10.
- There may be health benefits beyond endorphins and vitamin D production in sun exposure that research is unable to identify at this time11.
On days that individuals do not sunbathe, the Vitamin D Council recommends the following daily maintenance doses:
- Children: 1,000 IU per 25lbs of body weight.
Notes: Recommendation applies up to 125 lbs.
- Adults: 5,000 IU (including pregnant and breastfeeding mothers)
Notes: If obese, consider a higher dose. If pregnant or breastfeeding, it is important to check blood levels and to make sure the mother is sufficient (50 ng/ml). If the mother is sufficient, then the weaning infant does not need to supplement.
- Upper limit: 10,000 IU
Notes: If dosing at 10,000 IU/day or higher, the Vitamin D Council recommends 25(OH)D testing every 3 months for the first year, every 6 months thereafter.
These recommendations are based on dose response research, where 25(OH)D levels were measured after various daily dosing regimens. These recommendations will typically raise the average and healthy individual to blood levels around 50 ng/ml12,13,14. The Vitamin D Council makes these recommendations with the intention to meet the standards set in its “Blood Levels” section and not based on health outcome controlled trials.
Since vitamin D status is determined by blood levels and not dose, it is important to set a maintenance dose that achieves a targeted blood level first and foremost, and not select a maintenance dose intrinsically/arbitrarily. If an adult, for example, can achieve a blood level of 50 ng/ml on 3,500 IU/day, then that adult should take 3,500 IU/day. If an adult requires 8,000 IU/day to achieve a level of 50 ng/ml, however, then that adult should forego the 5,000 IU/day recommendation.
While testing is preferable, it is not necessary to test for blood levels of vitamin D. 5,000 IU/day will place the majority of adults into the sufficient reference range of 40-80 ng/ml.
The Vitamin D Council recommends daily doses over loading doses, as that mimics more closely physiologic production of vitamin D in response to sun exposure.
The Vitamin D Council recommends vitamin D3 (cholecalciferol) over D2 (ergocalciferol) for the following reasons:
- Vitamin D3 is the type of vitamin D the human body produces in response to sun exposure. Vitamin D2 supplements are produced by irradiating fungus9.
- Research has shown that the body prefers vitamin D3 over D2 when both forms are readily available in the body15.
- Research has shown that vitamin D3 is more efficacious in reducing mortality risk than D216. Research has also shown than vitamin D3 is more efficacious in reducing the risk of fractures and falls than D217.
- Haddad, JG, and KJ Chyu., “Competitive protein-binding radioassay for 25-hyrdroxycholecalciferol.” Jounral of Clinical Endocrinology, 1971.
- Luxwolda, MF, RS Kuipers, IP Kema, DA Janneke Dijck-Brouwer, and FA Muskiet. “Traditionally living population in East Africa have a mean serum 25-hyrdroxyvitamin D concentration of 115 nmol/l.” British Journal of Nutrition, 2012.
- Vieth, R. “The Pharmacology of Vitamin D, Including Fortification Strategies.” In Vitamin D, Second Edition, by Feldman D, Pike JW and Gloreieux FH, 995-1018. Elsevier Academic Press, 2005.
- Wagner, CL, TC Hulsey, D Fanning, M Ebeling, and BW Hollis. “High-Dose Vitamin D3 Supplementation in a Cohort of Breastfeeding Mothers and Their Infants: A 6-Month Follow-Up Pilot Study.” Breastfeeding Medicine, 2006.
- Vieth, R, Y Ladak, and PG Walfish. “Age-related changes in the 25-hydroxyvitamin D versus parathyroid hormone relationship suggest a different reason why older adults require more vitamin D.” Journal of Clinical Endocrinology and Metabolism, 2003.
- Bischoff-Ferrari, HA, A Shao, B Dawson-Hughes, J Hathcock, E Giovannucci, and WC Willett. “Benefit-risk assessment of vitamin D supplementation.” Osteoporosis International, 2010.
- Jacobsen, RB, BW Hronek, GA Schmidt, and ML Schilling. “Hypervitaminosis D Associated with a Vitamin D Dispensing Error.” The Annals of Pharmacotherapy, 2011.
- Holick, MF, TC Chen, Z Lu, and E Sauter. “Vitamin D and skin physiology: a D-lightful story.” Journal of Bone and Mineral Research, 2007.
- Holick, M. “Photobiology of Vitamin D.” In Vitamin D, by D Feldman, Pike JW and Glorieux FH, 37-45. Elsevier Academic Press, 2005.
- Clemens, TL, JS Adams, SL Henderson, and MF Holick. “Increased skin pigment reduces the capacity of skin to synthesise vitamin D3.” The Lancet, 1982.
- Becklund, BR, KS Severson, SV Vang, and DeLuca HF. “UV radiation suppresses experimental autoimmune encephalomyelitis independent of vitamin D production.” Proceedings of the National Academy of Sciences of the United States of America, 2010.
- Garland, CF, CB French, LL Baggerly, and RP Heaney. “Vitamin D supplement doses and serum 25-hydroxyvitamin D in the range associated with cancer prevention.” Anticancer Research, 2011.
- Heaney, RP, KM Davies, TC Chen, MF Holick, and MJ. Barger-Lux. “Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol.” American Journal of Clinical Nutrition, 2003.
- Pludowski, P, et al. “Vitamin D Supplementation and Vitamin D Status in Infants: A Prospective Cohort Observational Study.” Journal of Pediatric Gastroenterology and Nutrition, 2011.
- Heaney, RP, RR Recker, J Grote, RL Horst, and LAG Armas. “Vitamin D3 is more potent than vitamin D2 in humans.”Journal of Clinical Endocrinology and Metabolism, 2011: 96(3):E447-52.
- Bjelakovic, G, et al. “Vitamin D supplementation for prevention of mortality in adults.” Cochrane Database Systematic Review, 2011.
- Bischoff-Ferrari, HA, et al. “Prevention of nonvertebral fractures with oral vitamin D and dose dependency: a meta-analysis of randomized controlled trials.” Archives of Internal Medicine, 2009.