Examining a patient’s blood for vitamin D levels has become common
practice, with many millions of tests performed annually in the US.
Based on the current standards of normal—30 ng/mL or greater—between 50
and 90 percent of adults and children are considered deficient in
vitamin D.1-5 Even people who are exposed to large amounts of
sunlight do not meet the standards for sufficiency. For example, after a
spring and summer in sunny California and a trip to Costa Rica this past
July (2010) with hours spent intentionally sunbathing, Mary McDougall
had a vitamin D test run in August of 2010. She failed, based on
commonly reported standards, with a value of 29.6 ng/mL. Many
well-meaning doctors would have told her she was not in good health and
in need of supplementation with vitamin D pills, perhaps for a lifetime.
Mary is not an unusual example of well-sunned people failing this
commonly prescribed test. Similar results were found during a study of
active young people living in Hawaii with an average sun exposure of 29
hours a week. Even with all that vitamin D-promoting solar radiation, 51
percent of the group failed to meet sufficiency levels of 30 ng/mL.6 The
highest reported level was 62 ng/mL and several people had values below
20 ng/mL. Another study of 495 women with an average age of 74 years,
living in Hawaii, a geographical area with high environmental UV
irradiance, found 44 percent of subjects had vitamin D values of less
than 30 ng/mL, but none were below 10 ng/mL; and there was little
evidence of seasonal variation of vitamin D levels.7
Commonly Reported Standards for Blood Vitamin D Levels:
25-hydroxy vitamin D, reported as ng/mL.
10 or less
Deficiency: 20 or less
Insufficiency: 20 to 29
Sufficiency: 30 to 80
Above recommended: 81 to 199
Toxic: above 200
Based on recent reviews, adequate, I believe, is 20 ng/mL or
greater (see below).
To convert ng/mL to nmol/ml, multiply by 2.496.
have been reported to occur, so more than one reading should be
requested before any drastic actions are taken, like accepting a
lifetime of medication.
Normal Values for Vitamin D Are Set Too High
Normal levels are determined by comparing the effects of various
levels of vitamin D in the blood to parameters of bone health, such as
the body’s levels of parathyroid hormone (PTH), the ability of the
intestine to absorb calcium, and a person’s bone mineral density (BMD).
Recent reviews of the scientific literature have come to the conclusion
that the level set as normal (30 ng/mL or greater) is unsubstantiated
and in need of revision. Consider these comprehensive reports:
A review paper titled “Vitamin D Insufficiency” by Clifford Rosen
published in the January 20, 2011 issue of the New England Journal of
Medicine found “…the IOM (Institute of Medicine) report, based on
evidence from observational studies and recent randomized trials,
suggests that a serum level of 20 ng per milliliter of 25-hydroxy-
vitamin D would protect 97.5% of the population against adverse skeletal
outcomes such as fractures and falls.”5
An editorial in the January 2011 issue of the American Journal of
Clinical Nutrition reviewed a series of studies of children and
found that a vitamin D level above 12 ng/mL had no benefit on calcium
absorption and above 20 ng/mL there was no evidence on improved bone
A recent United
Kingdom consensus vitamin D position statement
indicates there is currently no standard definition of an optimal
concentration of vitamin D, and that concentrations below 10 ng/mL
should indicate deficiency.9
Widespread recommendations for testing vitamin D levels using a
standard that is too high to achieve is another example of disease
mongering—where healthy people are turned into patients. The net
effect is these newfound patients now spend more money on doctors’
visits, vitamin D tests, and supplements. My conclusion, based on the
scientific research, is that normal should be considered 20 ng/mL or
greater, a standard that most children and adults already meet. People
failing to reach this acceptable level need to expose themselves to more
Sunlight Is the Source of Vitamin D
Vitamin D is a hormone that is naturally produced within the body
with the help of the ultraviolet radiation from sunshine. Humans had
their origin in lands near the equator and had darkly pigmented skin
appropriate for a high intensity of solar radiation. As people migrated
from equatorial zones to greater latitudes, north and south, the
pigmentation of their skin decreased in order to allow more sunlight to
penetrate for D synthesis. This adaptation allowed people to move to
parts of the world as far north as Alaska, where sunlight is marginal
even during the summer months.
Except for some oily fish swimming in the waters of higher latitudes,
vitamin D does not naturally occur in our food supply. The exception of
oily fish demonstrates how natural environments support their
inhabitants—in this case fish eating provides the preformed hormone
vitamin D to people (and polar bears) living with very little sunlight
almost all year long.
Outside of the natural production of vitamin D by sunlight and that
found in oily fish, the only other substantial sources of vitamin D come
from supplements sold as pills or fortified foods. The most well known
food to which synthetic vitamin D is added during production is cow’s
Sunshine Is Essential for Good Health
Insufficient sunlight unquestionably results in two serious and
related diseases: rickets and osteomalacia. Abundant sunshine exposure
has also been associated with less risk of heart disease, common
cancers, multiple sclerosis, and other medical conditions. A review
published in the March 23, 2011 issue of the New England Journal of
Medicine stated that, “For outcomes beyond bone health, however,
including cancer, cardiovascular disease, diabetes, and autoimmune
disorders, the evidence was found to be inconsistent and inconclusive as
The association between low vitamin D and common diseases is most
certainly due to the confounding factor of food. People living in sunny
equatorial regions eat a starch-based diet whereas populations living at
higher latitudes, where sunshine is less abundant, eat more animal
foods, dairy and meat products. An unhealthy diet causes heart disease,
cancers, multiple sclerosis and other chronic diseases of Westerners.
However, this obvious conclusion should not diminish the importance of
How Much Sun Do You Need?
Overexposure to sunshine, resulting in skin damage, should be
avoided. That said, when the entire body is exposed to enough solar
radiation to cause the skin to become slightly pink (reddened)—an amount
referred to as the minimal erythemic dose (MED)—then the exposed
skin will release 10,000–20,000 IU of vitamin D into the circulation
within 24 hours of exposure.11 Vitamin D made in the skin lasts at least
two to three times longer in the circulation compared to taking vitamin
D as a supplement.12 Therefore, the human body has a highly efficient
capacity to make vitamin D with minimal sun exposure. Compare the
effects of supplements in order to get some idea of the potency of
sunlight to raise vitamin D levels in the blood: In general, for every
100 IU of vitamin D taken in, there is an increase of slightly less than
1 ng/mL in the serum level of 25-hydroxy-vitamin D.11
In practical terms, a person living in Boston who is not suntanned
and is fair-skinned will receive their total body MED from just 10 to 12
minutes of midday, July, summer sun. A darker-skinned Asian Indian will
require three times this exposure in order to receive their total body
MED. Very darkly pigmented people, such as blacks, will require 5 to 10
times more solar radiation than a white person. Vitamin D made in the
spring, summer, and fall months is efficiently stored in the body fat
and supplies people’s needs during winter months. The
next best choice
after natural sunlight would be to use artificial sunlight (sun beds,
I do not recommend taking vitamin D pill supplements (pills or
liquids) for most people because they provide little benefit in terms of
bone health and have concerning side effects.9 The overall harmful
effects caused by nutritional imbalances created by taking these pills
are far from fully understood; however, there is sufficient evidence
that taking vitamin D by mouth may increase your risk of heart disease,
several forms of cancer, and kidney stones. In addition, recent studies
have suggested levels of 25-hydroxy-vitamin D above 60 ng/mL are
associated with an increased risk of pancreatic cancer, vascular
calcification, and death from any cause.10
These days many people fail to get adequate sun because of their dark
skin pigmentation, living in high latitudes, wearing clothes, and
working indoors. My initial response to a failed vitamin D test is to
not take vitamin supplements, but rather to get outside, get more naked,
and get closer to the equator on vacations. I highly recommend a
Costa Rica McDougall Adventure
trip at least once a year for
optimal sunshine and excellent food.
1) Parry J, Sullivan E, Scott AC. Vitamin d sufficiency screening in
preoperative pediatric orthopaedic patients. J Pediatr Orthop.
2) Lee JH, Gadi R, Spertus JA, Tang F, O'Keefe JH. Prevalence of
Vitamin D Deficiency in Patients With Acute Myocardial Infarction. Am
J Cardiol. 2011 Mar 23.
3) Long AN, Ray MM, Nandikanti D, Bowman B, Khan A, Lamar K, Hughes
T, Adams-Graves P, Williams-Cleaves B. Prevalence of 25-hydroxyvitamin D
deficiency in an urban general internal medicine academic practice.
Tenn Med. 2011 Jan;104(1):45-6, 52.
4) Gómez-Alonso C, Naves-Díaz ML, Fernández-Martín JL, Díaz-López JB,
Fernández-Coto MT, Cannata-Andía JB. Vitamin D status and secondary
hyperparathyroidism: the importance of 25-hydroxyvitamin D cut-off
levels. Kidney Int Suppl. 2003 Jun;(85):S44-8.
5) Rosen CJ. Vitamin D Insufficiency. N Engl J Med. 2011 Jan
6) Binkley N, Novotny R, Krueger D, Kawahara T, Daida YG, Lensmeyer
G, Hollis BW, Drezner MK. Low Vitamin D Status despite Abundant Sun
Exposure. J Clin Endocrinol Metab. 2007 Jun;92(6):2130-5.
7) Pramyothin P, Techasurungkul S, Lin J, Wang H, Shah A, Ross PD,
Puapong R, Wasnich RD. Vitamin D status and falls, frailty, and
fractures among postmenopausal Japanese women living in Hawaii.
Osteoporos Int. 2009 Nov;20(11):1955-62.
8) Abrams SA. Vitamin D requirements in adolescents: what is the
target? Am J Clin Nutr. 2011 Mar;93(3):483-4. Epub 2011 Jan 26.
9) Shaw N. Vitamin D and bone health in children. BMJ. 2011
Jan 25;342:d192. doi: 10.1136/bmj.d192.
10) Manson JE, Mayne ST, Clinton SK. Vitamin D and Prevention of
Cancer — Ready for Prime Time?
N Engl J Med. 2011 Mar 23.
11) Hollis BW. Circulating 25-hydroxyvitamin D levels indicative of
vitamin D sufficiency: implications for establishing a new effective
dietary intake recommendation for vitamin D. J Nutr. 2005
12) Haddad JG, Matsuoka LY, Hollis BW, Hu YZ, Wortsman J. Human
plasma transport of vitamin D after its endogenous synthesis. J Clin
Invest. 1993 Jun;91(6):2552-5.
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