Low Vitamin D: A Global Concern
Recent studies suggest that vitamin D is much more important in fighting off disease than previously thought. Being deficient in this vitamin puts one at risk of diseases such as cancer, osteoporosis, and multiple sclerosis. Chances are that if you live in a northerly geographic region you do not get enough vitamin D. Persons who live a rather sedentary lifestyle and do not get outside for at least a 15-minute daily walk in the sun are in the same position. Latinos, African-Americans and others with dark skin tend to have much lower levels of vitamin D, as do people who are overweight or obese. All around the world millions of persons suffer from vitamin D deficiency. This phenomenon is so common that it affects persons on every continent, of all ethnic groups, and across all ages. Some surveys suggest that perhaps half of the world’s population has inadequate blood levels of vitamin D. Sadly, physicians, even in industrialized countries, are seeing the resurgence of rickets, the bone-weakening disease that had been largely eradicated through vitamin D fortification.
As with most research findings, there is plenty of debate. Indeed, as opposed to what many people think, there are few certainties in science; its nature is to be open to criticism, discussion, and revision. The Institute of Medicine (IOM) released a report in November 2010 which recommends a daily vitamin D intake of 600 IU per day, for people ages 1 to 70, and 800 IU, for people over age 70—the report referred to persons living in the U.S. and Canada. The report also recognized the safety of vitamin D by increasing the upper limit from 2,000 to 4,000 IU per day, and acknowledged that even at 4,000 IU per day, there was no good evidence of harm.
Some in the scientific community believe the new guidelines are too conservative about the intake, and that they do not give due consideration to the latest findings about vitamin D and health. They contend that the new guidelines are not enough to prevent chronic disease, and they are not sufficient to help those who have problems with their bones. This is an important debate, and in order to understand it better it is necessary to know the origins of vitamin D and how it functions in the human body.
Vitamin D Sources and Function
Our body makes vitamin D and it is also a nutrient we eat. The body produces vitamin D from cholesterol, which itself is triggered by sun lighting on the skin. Yet many persons do not make enough vitamin D from the sun, persons with darker skin, those who are overweight, and persons who use products that block sunlight being among them. Correctly applied sunscreen reduces our ability to absorb vitamin D by more than 90 percent.
To be sure, not all sunlight is of the same quality and intensity: The sun’s ultraviolet B (UVB) rays—the so-called “tanning” rays, and the rays that trigger the skin to produce vitamin D—are stronger near the equator and weaker at higher latitudes. Indeed, persons who live in places prone to considerable cloudiness and rain can suffer from vitamin D deficiency. The other way we get vitamin D is to eat food that contains a lot of it. However, few foods are naturally rich in vitamin D, so the biggest dietary sources of vitamin D are fortified foods and vitamins supplements.
Vitamin D helps the body absorb and retains calcium and phosphorus, which are critical elements for building bone. Laboratory studies show that vitamin D can reduce cancer cell growth, can increase muscle strength, and can help control infections. There may yet be other functions for vitamin D, and scientists continue to explore the many other uses for this important substance.
New Vitamin D Research: Beyond Building Bones
Vitamin D research has proved to be of considerable fecundity. Although there have been many reports issued over the years, there are only a few that offer enough evidence to constitute a clear medical breakthrough. Here we provide the more promising areas of vitamin D research, highlighting the complex role of vitamin D in disease prevention—and the many unanswered questions that remain.
Vitamin D and Bone and Muscle Strength
A number of random trials have shown that high doses of vitamin D supplements help reduce bone fractures. A summary of the evidence comes from a combined analysis of 12 fracture prevention trials that included more than 40,000 elderly people, most of them women. Researchers found that high intakes of vitamin D supplements—of about 800 IU per day—reduced hip and non-spine fractures by over 20 percent, while lower intakes (400 IU or less) failed to offer any fracture prevention benefit.
It has been shown that vitamin D may also help increase muscle strength, which can help prevent elderly persons from falling, a common problem that leads to increased rates of disability and death among them. A combined meta-analysis found that taking 700 to 1,000 IU of vitamin D per day lowered the risk of falls by 19 percent; the combined studies also show that taking 200 to 600 IU per day offered no such protection. Based on this data, the International Osteoporosis Foundation recommends that adults over age 60 maintain vitamin D blood levels of 30ng/ml. This means that most people will need vitamin D supplements of at least 800 to 1,000 IU per day, and possibly higher, to reach these levels.
Vitamin D and Heart Disease
The heart, as a skeletal muscle, is a receptor of vitamin D. A number of studies have found that lack of vitamin D is linked to heart disease. The Health Professional Follow-Up Study observed the vitamin D blood levels in nearly 50,000 men who were healthy. They followed the same group for 10 years and found that men who were low in vitamin D were twice as likely to have a heart attack as men who had adequate levels of vitamin D. Other studies have linked low vitamin D levels to an increased of heart failure, sudden cardiac death, stroke, overall cardiovascular disease, and cardiovascular death. There is some evidence that vitamin D plays a vital role in controlling blood pressure and preventing artery damage. This goes some ways in explaining the findings above. However, more research is needed before a sounder conclusion can be made.
Vitamin D and Cancer
Nearly 30 years ago, researchers discovered an interesting correlation between colon cancer deaths and geographic location. They found that people who lived at higher latitudes, such as in the northern U.S. or Canada, had higher rates of death from colon cancer than people who lived closer to the equator. The sun’s UVB rays are weaker at higher latitudes, and in turn, people’s vitamin D levels in these high latitude locales tend to be lower. Researchers formed the hypothesis that vitamin D deficiency can lead to an increased risk for getting colon cancer
Some time has passed, but dozens of studies suggest a relationship does exist between low vitamin D levels and increased risks of colon and other cancers. The evidence is strongest for colorectal cancer, with observational studies have found that persons with lower vitamin D levels are at higher risk of getting such diseases. Vitamin D levels may also predict cancer survival, but there is as yet little evidence to support this. However, it is not yet certain that taking vitamin D supplements necessarily lowers the risk of contracting cancer. This latter idea will be tested in the VITAL trial. The VITAL trial will look specifically at whether vitamin D supplements lower cancer risk. However, it is likely to be years before the trial produces any results. Additionally, the VITAL trial could fail to detect a real benefit of vitamin D. There are several reasons for this. First, if people in the placebo group decide to take their own vitamin D supplements, the differences between the placebo group and the supplement group could be minimized. Second, the study may not follow participants for a long enough time to show a cancer prevention benefit; or study participants may be starting supplements too late in life to lower their cancer risk.
In any case, given the evidence now on hand, 16 scientists have circulated a “call for action” on vitamin D and cancer prevention. Given the high rates of vitamin D inadequacy in North America, the strong evidence for reduction of osteoporosis and fractures, the potential cancer-fighting benefits of vitamin D, and the low risk of vitamin D supplementation, these scientists recommend vitamin D supplementation of 2,000 IU per day. The Canadian Cancer Society has also recommended that Canadian adults consider taking vitamin D supplements of 1,000 IU per day during the fall and winter. They also recommend that people who are at high risk of having low vitamin D levels because of old age, dark skin, or geographic location take vitamin D supplements year round.