From clinical journals to the daily newspaper, everyone is talking about vitamin D. In many ways, headlines about a vitamin whose existence has been known for decades seem surprising. Nevertheless, this freely available nutrient is causing quite a stir in medical and nutritional circles. Vitamin D deficiencies are being aggressively explored for their potential links to cancer, coronary artery disease, diabetes, falls, and cognitive disorders.
Background
The relationship between sunlight exposure and vitamin D levels has been acknowledged for more than 60 years. Forty year later, the presence or absence of vitamin D from sunlight was linked to cancer occurrence.1
At the same time studies on the benefits of vitamin D were beginning, concerns over UV exposure from sunlight began to emerge. Even though the literature contains consistent reports of the benefits of vitamin D from the early 1980s to the present, news of dangers associated with sun exposure took center stage, and the heavy use of sunscreen has prevailed for the past two or three decades.
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Science
Vitamin D is a potent steroidlike hormone that affects more than 200 human genes.2 It has actions similar to those of a broad-spectrum antibiotic and a repair and maintenance chemical.2 Multiple studies have confirmed the effect of vitamin D on cell proliferation, calcium and phosphorus regulation, and the downregulation of hyperproliferative cells characteristic of malignancy.3
Humans get vitamin D from sunlight and food. Vitamin D obtained from sunlight exposure is already in the active form of vitamin D3, whereas vitamin D in food must be converted from vitamin D2.3 Both sources initiate a conversion process in the liver that transforms vitamin D2 or D3 into 1,25-dihydroxyvitamin D, which is the active metabolite used by the rest of the body.4
In the United States, identifying a population of individuals that has a sufficient blood level of vitamin D has become difficult.5 Geographically, North America experiences less direct sunshine than areas closer to the equator. Many of the population-based trials were conducted in the upper latitudes of North America and found the typical serum vitamin D level of participants significantly deficient.
Increasing BMI and age are independent risk factors for vitamin D deficiency.5 Vitamin D is a fat-soluble vitamin. Thus, the higher the body’s fat content, the wider the storage distribution and the lower the serum level of vitamin D. Mechanisms in the skin that convert sunlight exposure to active vitamin D decrease with age, making the process less efficient.5
A meta-analysis of independent randomized, controlled trials looked for all-cause mortality. These trials used a range of vitamin D supplementation for the experimental groups at a trial-adjusted level of 528 IU/day. A definite inverse correlation between vitamin D supplementation and relative risk of mortality was observed.6
Vitamin D has long been known to play an essential role in bone metabolism. Chemically, vitamin D in the active form is essential for calcium and phosphorus absorption and deposition in healthy bone matrix. One study found calcium absorption was 65% higher when serum vitamin D levels were higher.3 Researchers have demonstrated a 25%-35% fracture reduction in patients with therapeutic levels of serum vitamin D.3
Research shows the potential of vitamin D to dramatically reduce cancer risk. An estimated 50% of colon cancers and 30% of breast cancers could be prevented with sustained adequate serum levels of vitamin D.3 Other researchers looked at prostate and ovarian cancers and found a similar relationship.3 In one trial, nearly 1,200 postmenopausal women who received daily supplements of vitamin D 1,100 IU had a 60%-77% reduction of all forms of cancer.1
Multiple animal studies and population studies show a strong correlation between vitamin D levels and conditions such as autism, multiple sclerosis, and Alzheimer’s dementia.3,6,7
Safety
Since vitamin D occurs naturally in the body, it is inherently safe. However, because of its fat solubility, ingestion of too much vitamin D leading to toxicity is possible. Serum vitamin D levels in excess of 70 ng/mL are considered potentially dangerous.2 Toxicity results from the excessive metabolism of calcium that is triggered by the vitamin D. This increased calcium begins to embed in solid organs and results in end-organ damage.2
How supplied, dosage
For children, the recommended daily intake of vitamin D is 400 IU until or unless the child is consuming at least one liter of vitamin D-fortified milk per day. The recommended daily dose for adults is up to 2,000 IU.4 Serum levels should achieve a minimum of 30 ng/mL.7 Gastric absorption of the supplemental form of vitamin D is better with oil-filled capsules than tablets.4
In healthy children and adults, forearm-skin exposure to sunlight for 15-20 minutes daily will generate the equivalent of 1,000 IU of vitamin D3.8 Fatty fish and fish liver oils are the foods highest in vitamin D. Cod liver oil, herring, salmon, and catfish are among the foods richest in vitamin D.
References
1. Lappe JM, Travers-Gustafson D, Davies KM, et al. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr. 2007;85:1586-1591.
2. Cannell JJ, Hollis BW. Use of vitamin D in clinical practice. Altern Med Rev. 2008;13:6-20.
3. Brown SE. Vitamin D and fracture reduction: An evaluation of the existing research. Altern Med Rev. 2008;13:21-33.
4. Moyad MA. Vitamin D: a rapid review. Dermatol Nurs. 2009;21:25-30, 55.
5. Autier P, Gandini S. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Arch Intern Med. 2007;167:1730-1737.
6. Cannell JJ. Autism and vitamin D. Med Hypotheses. 2008;7:750-759.
7. Raghuwanshi A, Joshi SS, Christakos S. Vitamin D and multiple sclerosis. J Cell Biochem. 2008;105:338-343.
8. Bordelon P, Ghetu MV, Langan RC. Recognition and management of vitamin D deficiency. Am Fam Physician. 2009;80:841-846.
All electronic documents accessed December 14, 2009.
