The long, dark days of another winter have come and gone. Tens of millions of Americans would be surprised to learn that winter has left them deficient in vitamin D. Your chances of being one of them are probably much greater than you imagine.
Vitamin D is synthesized in the skin in response to sunlight exposure, but few people achieve optimal levels this way, in part due to the limited ultraviolet light available during the winter months. This seasonal deficit is compounded by the fact that many people avoid sun exposure during the spring and summer months because of concern about premature skin aging and cancers like melanoma. Alarming new research suggests that these factors are contributing to a year-round epidemic of vitamin D deficiency, particularly in elderly adults.
Vitamin D does far more than promote healthy teeth and bones. Its role in supporting immunity, modulating inflammation, and preventing cancer make the consequences of vitamin D deficiency potentially devastating. A growing number of scientists who study vitamin D levels in human populations now recommend annual blood tests to check vitamin D status.
In this article, we examine the factors that contribute to the widespread prevalence of vitamin D deficiency, the latest studies supporting vitamin D’s critical role in preventing disease, and how much supplemental vitamin D you need to achieve optimal blood levels.
Vitamin D Deficiency: An Overlooked Epidemic
Vitamin D is a fat-soluble prohormone—that is, it has no hormone activity itself, but is converted to a molecule that does, through a tightly regulated synthesis mechanism. Its two major forms are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). Vitamin D also refers to metabolites and other analogues of these substances. Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B radiation.
While vitamin D is best known for promoting calcium absorption and bone health, researchers have recently discovered important new roles for this versatile vitamin.1 As an active hormone,2 vitamin D is now seen as playing a central role in controlling immunity and inflammation,1,3,4 two vital processes that are tied to a host of age-related disease conditions.5-10
Just as scientists are discovering critical new roles for vitamin D, they are also finding that shockingly few people have blood levels of vitamin D adequate to support their daily needs.5,6 One leading researcher has referred to this deficit as a “vitamin D epidemic.”7 Estimates of the percentage of US adolescents and adults who are vitamin D deficient range from 21% to 58%,11 while as many as 54% of homebound older adults are believed to be vitamin D deficient.12
Because vitamin D3 is obtained in humans primarily as a result of exposure to sunlight,8 this puts people living outside the tropics at particular risk for vitamin D deficiency, especially from late fall to early spring.9 Further compounding the problem, many public health officials are concerned that their warnings about avoiding the sun because of skin cancer risk may in fact be causing people to limit their sun exposure to an unhealthy extent.10,13
Because sun exposure does pose significant health risks, and most Americans live outside of the regions where they can get adequate sun in winter, perhaps the best way to address this dilemma is by paying close attention to your blood levels of vitamin D and optimizing them through appropriate supplementation. Life Extension recommends that adults check their blood levels and supplement with enough vitamin D3 to achieve optimal blood levels.6-8
To meet all of the body’s needs for proper vitamin D activity, many scientists now advocate supplementing with doses that are considerably higher than the minimums currently recommended by the Institute of Medicine.14 While vitamin D can be obtained through a few dietary sources such as fish, eggs, and dairy products, these foods fail to provide the daily levels required by most individuals, thus necessitating vitamin D supplementation.
Applications for Preventing and Treating Cancer
Strong epidemiological data now implicate low vitamin D levels in at least 16 different malignancies.47 Powerful clinical evidence indicates that vitamin D may be useful in preventing and even treating colon and prostate cancers, while suggestive evidence points to its effects in countering lung, breast, skin, and other cancers.16,47
Twenty-five years of research suggests that detecting and correcting vitamin D deficiency may be especially important in averting colon cancer, a disease that claims approximately 56,000 lives each year in the United States.48
An early study of 1,954 men found that those with the lowest vitamin D intake had more than double the risk of colon cancer compared to men with the highest intake.49 Colon cells reproduce very quickly, placing them at risk for becoming malignant. When active vitamin D was applied to colon cells in culture, reproduction rates fell by 57% in normal colon tissue and by 52% in patients with familial adenomatous polyposis, an inherited syndrome characterized by many pre-cancerous polyps.50 In a laboratory study, pretreatment with vitamin D made colon cancer cells easier to kill with hydrogen peroxide and other natural oxidants present in the bowel.51
A large randomized trial from 2003 helped to establish a clinical role for vitamin D in preventing colon cancer.52 Eight hundred three subjects with previous colorectal adenomas (which can lead to cancer if they recur) were given calcium supplements or placebo, and their rates of adenoma recurrence were measured. Calcium supplements reduced the risk of adenoma recurrence by 29% in subjects with normal D levels. This study demonstrated that both calcium and adequate vitamin D levels are needed to reduce colon cancer risk.
In a 2006 study,53 researchers surgically divided individual adenomatous (potentially precancerous) polyps, removing approximately 50% from 19 patients. They marked the remnants of the polyps in the intestine so they could identify them later, and studied cell proliferation in the polyp tissue before and after six months of treatment with oral vitamin D3 (400 IU) and calcium carbonate (1500 mg, three times daily) or placebo. Adenomas from patients treated with calcium and vitamin D3 showed marked declines in cell proliferation and other signs of cancerous change, while there was no change in tissue taken from the control patients.
Scanning electron micrograph of human colon carcinoma.
Cancer prevention specialists at the University of California recently conducted an extensive review of scientific papers published worldwide between 1966 and 2004. Their analysis suggested that taking 1000 international units (IU) of vitamin D3 daily lowers an individual’s risk of developing colorectal cancer by 50%. The researchers recommended increased intake of vitamin D3 as an inexpensive, non-toxic preventive therapy for colon cancer. Specifically, they hope to see the federal government officially recommend intake of 1000 IU per day of vitamin D3 for cancer prevention.48