Wellness: Do the D
When we talk about maintaining health and wellness, we are generally referring to increasing both quantity and quality of life. Critical to both pursuits are not only the maintenance of our bones, muscles and major organs, but also our cellular health—something that's not only much harder to keep track of in a visual or even a somatic sense, but also more difficult to support directly by managing our lifestyle and nutrition.
The more we learn about genes, chromosomes and other sub-cellular structures that contain the codes which govern the replication of our cells, however, the more we also come to understand some of the processes involved in sustaining that replication, be they metabolic, electro-chemical or even photosynthetic.
Much new information has emerged recently about the beneficial effects of vitamin D and its mineral partner in cellular action, calcium. For decades, most of us have understood the basic benefits of these actors, having witnessed as a society the epidemics of rickets, osteoporosis and other deficiency-related diseases that emerged during the industrial revolution, when most people began to work indoors and wear more clothes outdoors. The natural absorption of ultraviolet sunlight, and hence the synthesis of natural vitamin D in human skin, became much more limited, especially in northern latitudes. In an effort to reduce this, many foods were eventually fortified with the nutrient and remain so to this day, including milk, yogurt, cereal, juices, margarine and bread. Many recent studies continue to demonstrate the vitamin's preventive effects on a whole host of diseases.
Among the ailments thought to be related to deficiency in vitamin D are high blood pressure, tuberculosis, cancer (including colon and colorectal cancers, breast and ovarian cancers, pancreatic cancer and prostate cancer), periodontal disease, multiple sclerosis, chronic pain, seasonal affective disorder, peripheral artery disease, cognitive impairment (including memory loss) and several autoimmune diseases, including type 1 diabetes. Studies done over the past three decades have shown increases of cancer risk that vary from 30 to 77 percent in people who are vitamin D deficient (depending on the type of cancer studied), and in 2007 the Canadian Cancer Society recommended that all its country's adult citizens take a supplement of 1,000 IUs (International Units; 200 IUs equals 5 micrograms) of vitamin D daily. Vitamin D supplementation may also play a role in reducing the risk of, and even reversing, cardiovascular disease.
In the United States, the recommended daily allowance (RDA) of vitamin D for adults has been set by the FDA at 400 IUs, and 200 IUs has been designated as adequate for children. Most Americans do not consume this much, however, anv those living in northern latitudes in the U.S. can synthesize little or none from sunlight between November and March. In spite of a proliferation of fortified foods and beverages, the majority of the U.S. population is classified as being deficient in this vitamin unless they take supplements. The American Academy of Pediatrics recommends a minimum of 400 IUs even for infants, and the National Institutes of Health now recognize new data that may prompt them to increase their current "safe upper limit" of the supplement from 2,000 IU to 10,000 IU or more, pending results of a study by the Institute of Medicine expected this spring.
Vitamin D comes in several forms, but the most relevant to life as we know it are vitamin D2 and vitamin D3. Known collectively as calciferol, the variants present themselves in different life forms, vitamin D2 principally in plants, fungus and invertebrate animals, vitamin D3 in vertebrates (including humans). Either can be taken as a supplement, though some nutritionists believe D3 is more effectively utilized than D2 by the human body in important hormonal activity; however, for other species the opposite may be true. Natural production of D3 in human skin occurs in the lowermost layers of the epidermis, where UVB radiation acts photochemically (not unlike photosynthesis in plants) to convert it from 7-dehydrocholesterol, a common organic compound without which the vitamin could not be synthesized.
Melanin, the familiar compound responsible for skin pigmentation, is present (except in albinos) in the same epidermal layer where D3 is produced (stratum basale), and is a major factor in protection from the harmful effects of sunlight, particularly UVB radiation. Its primary action in the skin is the (typically highly efficient) conversion of harmful UV rays into innocuous, dissipated heat and minimization of released free radicals, which can lead to DNA damage and, ultimately, malignant melanoma. Unfortunately, the tradeoff is that generous amounts of melanin also (because they essentially act as light filters) slow natural vitamin D production. What this means to people is basically that those whose skin is melanin-rich (darker-skinned people) will need more prolonged exposure to sunlight to produce the same amount of D3 that a person of lighter skin would in a shorter time.
Good natural sources of ingestible vitamin D include several varieties of river, lake and ocean fish and fish byproducts, though the best of the lot seem to be herring, catfish and salmon, as well as the oft-lauded fish liver oils (the best known being cod liver oil). Eggs, beef liver and UV-irradiated mushrooms can also provide smaller amounts of vitamin D. Supplements are widely available in a variety of doses up to 2,000 IUs without a prescription, though most one-a-day options typically range from 400 to 1,000 IUs. It is possible to overdose on Vitamin D, which can cause hypercalcemia (a condition wherein the body absorbs too much calcium), and this can cause a range of problems from high blood pressure to urinary and kidney dysfunction. However, such instances are quite rare and generally result only from higher-dose prescription varieties of the supplement.
The latest wave of fascination with vitamin D centers mainly on its prophylactic and even potentially curative effects. Its role in cellular reproduction and the slowing of the aging process is also a subject of great interest to the scientific community, especially in this new age of genetic discovery and an ever-growing database and understanding of DNA-level cause-and-effect relationships. Vitamin D is considered an immunological moderator because of its effects on immune cell receptors. It helps to regulate immune cell behavior through both immune-enhancing and immunosuppressive functions, exhibiting characteristics that can have effects running the gamut from inhibiting the growth of cancer cells to invigorating macrophages (large white blood cells involved in immune function) that play roles in attacking viruses, bacteria and fungi. It has been shown that vitamin D deficiency can significantly increase the risk of infection in otherwise healthy bodies, creating vulnerability to diseases like influenza, pneumonia and tuberculosis.
Dr. Andrew Weil, the hale, classically-bearded author of numerous books on nutrition and healthy lifestyle, describes the vitamin's benefits:
"Vitamin D assists in the absorption of calcium and promotes bone mineralization, which may prevent or slow the progression of osteoporosis. It also helps to strengthen the immune system and protect against a number of serious diseases, including rickets and osteomalacia. Research suggests vitamin D may also provide protection from hypertension, psoriasis, several autoimmune diseases (including multiple sclerosis and rheumatoid arthritis), and reduce the incidence of fractured bones. In addition, growing evidence has demonstrated its important role in defending against cancer (studies link a deficiency of vitamin D to as many as 18 different cancers)."
Calcitriol, vitamin D's hormonally active form, is responsible for the vitamin's growing reputation as an anti-carcinogen, as it has been shown to induce death in cancer cells both in vitro (in a test tube) and in vivo (in living creatures). It is thought that, due to its action as a potent nuclear transcription factor (a substance that regulates the transfer of genetic information at the DNA level), it beneficially controls essential parts of the cell replication process, balancing them and especially assuring that an ideal level of apoptosis (programmed cell death) is constantly occurring. Without sufficient rates of apoptosis, uncontrolled cell proliferation can lead to the appearance and growth of cancer cells.
The management of healthy cell replication and the ongoing transfer of DNA sequences, as well as other critical genetic processes, has also associated vitamin D with slowing of the natural aging process. In 2009, researchers Elizabeth Blackburn, Carol Greider and Jack Szostak were awarded the 2009 Nobel Prize in Physiology/Medicine for their ongoing studies of telomeres and the enzyme telomerase. Telomeres are basically "tips" of repetitive DNA at the ends of chromosomes that have been referred to as "fuses," or clocks that time the natural life of cells. In some instances, longer telomeres have been associated with longer lifespans, and vitamin D has been shown to slow down the clock that shortens leukocyte (white blood cell) telomeres.
However, all such associations are quite complex; elevated amounts of telomerase promote the growth of "immortal" cells, which are usually cancer or other unwanted cells, and so the balance between extending cell life and restraining a cell's propensity for uncontrolled growth is a delicate one.
Many have been critical of the health care industry for not devoting more resources to the study of Vitamin D and its already proven effects on a host of vital bodily functions. Some have gone so far as to accuse drug companies of purposefully dragging their feet, sensing that the emergence of a relatively inexpensive compound as a widely-accepted preventative—or even a curative—with such broad-spectrum potential could be a threat to profits from the sale of remedial drugs and even high-cost cancer medicines.
Whether or not such suspicion has merit, the mounting evidence of vitamin D's beneficial effects is worth taking a look at and evaluating according to your own lifestyle and personal medical history. If a doctor says it's okay, start trying to eat more vitamin D-rich foods and taking supplements as soon as you can. The more information that comes out, the more it seems we all have everything to gain from it and nothing to lose.