Some reports suggest nearly half the world's population suffers from vitamin D deficiency, which is unsettling news given that a lack of vitamin D has been associated with a host of serious conditions: cancer, heart disease, diabetes, multiple sclerosis, tuberculosis and even depression, not to mention brittle bones and the common cold.
"It's a long list because the vitamin D steroid hormone affects different genes in different tissues," says John Cannell, founder of the Vitamin D Council and author of "Autism Causes, Prevention and Treatment: Vitamin D Deficiency and the Explosive Rise of Autism Spectrum Disorder."
"Vitamin D is a steroid hormone precursor that is made in the skin," Cannell explains. "The vitamin D steroid hormone activates up to 1,000 of the 21,000 active genes in the human genome. If the gene is in the brain, vitamin D affects the brain. If the gene is in the heart, vitamin D affects the heart. Thirty-seven different tissues in the human body utilize vitamin D and need it for adequate functioning."
Given the importance of vitamin D to the body, a growing number of studies highlight what an insufficient amount can mean to one's health.
In a study published Wednesday in BMJ, researchers tracked the blood samples of more than 95,000 participants for nearly 40 years and found that genes associated with permanent low levels of vitamin D raised the risk of early death. Throughout the study period, people with these genes had an increased mortality rate of 30 percent and a 40 percent higher risk of death from cancer.
While previous studies have shown a link between a vitamin D deficiency and increased mortality, the possibility that low levels of vitamin D were the result of poor health could have distorted those findings. For the first time, a causal relationship between a vitamin D deficiency and increased mortality was established.
In October, researchers revealed that in a study of patients who suffered from sudden cardiac arrest, 65 percent of those with low vitamin D levels suffered poor neurological outcomes six months after hospital discharge, compared with 23 percent of patients with healthy vitamin D levels. In addition, 29 percent of patients with low levels died six months after their cardiac attack, whereas all the patients with healthy vitamin D levels survived.
How does vitamin D, or a lack thereof, affect neurological function? "Vitamin D functions as a modulator in brain development and as a neuroprotectant through the association of neurotrophic factors," says study author Jin Wi, a professor at Yonsei University College of Medicine in Seoul, Korea. "Vitamin D deficiency causes neuronal apoptosis and hinders the growth and survival of neurons, leading to the impairment of neurological function. In patients resuscitated after sudden cardiac arrest, neurological dysfunction is caused mainly by excessive oxidative stress, free radicals and immune reaction. Vitamin D provides antioxidative mechanisms and regulates the immune system by reducing inflammatory cytokines."
Given their findings, Wi adds that "a vitamin D deficiency should be avoided, especially in people with a high risk of sudden cardiac arrest. People are at a higher risk if they have a personal or family history of heart disease, including heart rhythm disorders, congenital heart defects and cardiac arrest."
In an online issue of Neurology published in August, a study examined the vitamin D levels of 1,658 people over age 65 who were dementia-free. Nearly 200 of the subjects developed dementia, and slightly more than 100 had Alzheimer's disease after an average of six years.
The researchers discovered that when compared with subjects with normal levels of vitamin D, those with low levels had a 53 percent increased risk of developing dementia, while those with a severe deficiency had a 125 percent increased risk. Plus, people with lower levels of vitamin D were almost 70 percent more likely to develop Alzheimer's disease, while those with a severe deficiency were more than 120 percent more likely to do so.
How to Get Enough
The major source of vitamin D is exposure to the sun, which is why it earned the nickname "the sunshine vitamin." It's created in the skin, although "the amount of sunlight needed to synthesize adequate amounts of vitamin D varies, depending upon the person's age, skin color, sun exposure and underlying medical problems," says Shamim Shakibai, an internal medicine physician at Marina Del Rey Hospital in Marina del Rey, California. "The production of vitamin D from the skin decreases with age. In addition, people who have darker skin need more sun exposure to produce adequate amounts of vitamin D, especially during the winter months."
Due to the increased use of sunscreen, fewer people are getting the necessary sun exposure, making it a significant cause of vitamin D deficiency. One study found that sunscreen with an SPF of 15, when used properly, can reduce vitamin D formation by as much as 99 percent.
"Although people should always protect themselves from the harmful effects of the sun, the sun is a crucial source of vitamin D," says Damon Raskin, an internist based in Pacific Palisades, California. "Many people become deficient because of diet and a lack of sunlight."
Only a few foods, such as eggs (specifically the yolk) and fatty fish such as salmon, mackerel and tuna, are natural sources of the vitamin. "In the United States, commercially fortified cow's milk is the largest source of dietary vitamin D, while in other parts of the world, cereals and bread products are often fortified with vitamin D," Shakibai says.
Just how much vitamin D do you need? Recommendations vary, so consult your doctor. The National Institutes of Health suggest 600 international units a day for those ages 1 to 70. "In general, adults are advised to take a supplement containing 800 international units of vitamin D per day," Shakibai says. "[And] all infants and children are advised to take a vitamin D supplement containing 400 international units of vitamin D, starting within days of birth." Cannell adds: "The Vitamin D Council recommends safe, sensible sun exposure, and if that is not possible, [then] 5,000 IU a day."
It should be noted, though, that it's possible to take too much vitamin D. Referring to a source suggesting 50,000 IU a day, Cannell remarks that this "dose will make some people toxic, causing high blood calcium and renal failure with the calcification of internal organs."
Shakibai warns that vitamin D intoxication generally occurs after inappropriate use of vitamin D preparations. "It may occur in fad dieters who consume 'megadoses' of supplements or in patients who take vitamin D replacement therapy for malabsorption, renal osteodystrophy, osteoporosis or psoriasis," she says. "Vitamin D intoxication has been documented in adults taking more than 60,000 international units per day." Symptoms of vitamin D toxicity include nausea, vomiting, weakness, dehydration, constipation and poor appetite.
Whether one is getting enough vitamin D -- either through sun exposure, supplementation or food -- is a valid question for everyone to ask. As Shakibai points out and recent research continues to confirm, "Vitamin D plays an important role in many places throughout the body."