Vitamin D and Your Health: New Findings

Vitamin D is in the limelight (if not in the sunlight) these days. And not just for its role in creating strong bones. More and more studies are citing the wide-ranging health benefits of vitamin D, from improved cognitive functioning to prevention of cancer. In light of these findings, a new look at your vitamin D intake and that of your family’s intake, may be worthwhile. It wasn’t that long ago that experts considered our exposure to sunshine and intake of milk adequate for our vitamin D needs, and determined that taking in 2000 IU of D would be “toxic." Today, medical experts have doubled the recommended intake of vitamin D for babies and children, and many are now calling on a dramatic revision of adult doses, especially for older folks. What’s changed? Read on to learn more about the so-called “sunshine vitamin."

What is vitamin D?

Vitamin D is a fat soluble vitamin that is actually a member of a group of substances derived from the cholesterol molecule. Both vitamin D2 and D3 are found in the circulation of our bodies, but the amounts of each are dependent on our diet and the amount of skin exposure we get to ultraviolet-B radiation (UVB). The main function of vitamin D is to enable us to absorb calcium, and to a lesser extent, phosphorus. This in turn keeps things normalized for our bone mineralization, muscle contraction, nerve conduction, immune functioning, and general cellular function in all cells of our body.

When we don’t get enough vitamin D from the sun, it becomes an essential nutrient, that is, a nutrient that is required for normal body functioning that cannot be synthesized by the body and therefore must be obtained from a dietary source. There is actually no significant natural source of vitamin D from our diets. Very little D2 is available from plants, but more can be obtained from fortified foods, and vitamin D3 is found in fish oil.

The focus on vitamin D deficiency states began in the late 19^th and early 20^th centuries when we were mostly concerned with rickets, a widespread bone softening disease. This problem responded to vitamin D supplementation through sun exposure and foods with D. In the mid to late 20^th century, inadequate amounts of vitamin D were implicated in the development of osteopenia and osteoporosis. The problem with inadequate amounts of vitamin D was also found to be a contributing factor for muscle weakness and falls. In fact, more than half of individuals with a history of fracture have been found to have low vitamin D levels. Furthermore, low parathyroid levels are higher in the elderly which may also affect the skeleton. So, when you put together all the factors - lack of sun exposure, the biological consequences of aging, and a low vitamin D intake, the elderly are at high risk for problems.

Overall, women are more than twice as likely as men to have low levels of vitamin D. Many post-menopausal women with and without osteoporosis are deficient. This is a concern as they are already predisposed to osteoporosis because of decreasing estrogen levels. In the United States, it is estimated that 42 percent of African-American girls and women ages 15 – 49, and about 35 percent of all women ages 20 to 69 have low blood levels of vitamin D.

What are the potential health benefits of vitamin D?

The benefits for bone health are obvious but striking. Randomized trials using 700 to 800 IU/day of vitamin D (higher than the currently recommended 400 IU/day) found less fracture incidence, with and without supplemental calcium. This result is thought to be from better bone health and fewer falls due to greater muscle strength and better balance. One meta-analysis reported a 22% decrease in falls associated with vitamin D supplement use. Other studies have shown that vitamin D supplementation may contribute to gains in bone mineral density, and some have found a positive relationship between cognitive functioning and vitamin D levels, which may also influence the risk of falls and fracture. Inadequate vitamin D levels have also been associated with chronic musculoskeletal pain, which can be confused with conditions such as fibromyalgia. In these patients, supplementation may be useful in helping increase bone mineral density.

Recent studies are suggesting this important vitamin is the necessary factor for a number of effects on the body that were previously attributed only to calcium. In addition to skeletal benefits, the large number of effects on so many tissues is explained by vitamin D’s regulation of at least 150 specific nuclear receptors which regulate cell differentiation and growth. These effects may have implications for a wide range of diseases including: hypertension, senile dementia, cancer, diabetes, depression, immune deficiencies, multiple sclerosis, and other disorders.

Vitamin D expert Michael F. Holick, MD, PhD, of Boston University Medical Center claims that if women maintained high levels of vitamin D, they could reduce their risk of breast cancer as much as 50 percent; colorectal cancer up to 253 percent; and heart disease, stroke and peripheral artery disease more than 100 percent.

A recent clinical trial that focused on the bone health of 1,179 postmenopausal women living in rural Nebraska, found that subjects who took daily calcium supplements along with 1,100 IU vitamin D3 had a significantly lower incidence of cancer over 4 years compared with the placebo group.

What’s the sun’s role?

These days, D is not an easy vitamin to get. We’ve been well trained to avoid our best source while covering our bodies and using sunscreen to prevent skin cancer. (Wearing sunscreen of SPF 8 or more reduces the skin's ability to produce vitamin D by 95%). For people in the northern two-thirds of the country, it’s nearly impossible to get enough D from the sun between October and April. The latitude, season, and time of day all affect vitamin D synthesis, and heavy clouds, smoke or smog are also factors.

In addition, we’ve all cut back on the time we spend outdoors – from children to the elderly. The elderly are less efficient in making vitamin D2 and people with darker skin synthesize less vitamin D due to the melanin which gives skin its color. Furthermore, people who are obese have less D available to them because of the tendency of body fat to hold on to the vitamin, and people with fat malabsorption disorders such as Crohn’s disease and celiac disease may require more D.

How do we get enough vitamin D?

Given the conclusions of recent studies, many researchers are questioning the currently recommended levels of vitamin D intake, maintaining that the levels used to prevent rickets in children, are not enough to fight the serious health issues that may now be linked to low vitamin D levels. Not everyone agrees - partly because the need for more studies and partly because of the fears of toxicity. Some experts are concerned that higher vitamin D levels and calcium can raise the risk of kidney stones in susceptible people.

The tolerable upper intake levels (ULs) first published in 1997, lists 2,000 IUs for adults. However, many scientists have challenged these ULs saying that in healthy adults, a UL as high as 10,000 IU/day should be tolerated. Also, larger doses of D taken for a short time or periodically (e.g. 50,000 IU/week for 8 weeks) do not cause toxicity. The excess is stored and used as needed to maintain normal levels when vitamin D intake or sun exposure is limited.

There are two forms of vitamin D that have been used as supplements: vitamin D2 and vitamin D3. Scientific evidence shows that D3 is preferred because it is more readily absorbed. You can take vitamin D3 supplements on their own, as a multivitamin which usually contains 400 IU, or in a calcium/vitamin D combination. You should always talk with your healthcare provider about taking any supplements to prevent the risk of over dosage and toxicity.

Drinks like milk, soy milk, and some juices are fortified with vitamin D. For example, an eight-ounce glass of milk or fortified orange juice is supposed to contain 100 IU. Fish oil is the best food source and wild-caught (not farmed) oily fish like salmon and mackerel are high in D, but you also want to watch your intake of mercury. And eating fish with the bones is even better -- a cup of canned red salmon has about 940 IU. It is very unlikely that you can become toxic on dietary D unless large amounts of cod liver oil are consumed.

New adult guidelines are expected within the next couple of years, but many health care providers are now recommending blood levels of 30ng/ml (nanograms per milliliter). To achieve this they are advising taking a supplement of 800 - 1000 IU/day (or 1,700 IU from all sources of vitamin D). Current recommendations are for 200 IU/day for adults 19 – 50; 400 IU for those 51 to 70; and 600 IU for those 71 and older.

The American Academy of Pediatrics has recently doubled its recommended dosage of vitamin D to 400 IU for children, beginning in the first few days of life. This is important for breast-fed and partially breast-fed infants (as breast milk does not have enough D3), and for formula-fed babies who consume less than 32 ounces/day of vitamin D fortified formula. These recommendations extend to children and adolescents who do not get 400 IU of vitamin D per day through foods. The 400 IU amount is standard for children's multivitamins.

Stay tuned for more information and guideline recommendations as scientists continue to take a new look at an old vitamin.

Where's the D?