A suboptimal level of vitamin D may be a risk factor for prostate cancer. Achieving an optimal level may be a new way to help prevent prostate cancer or to slow or reverse advanced disease.
1. How does vitamin D affect the prostate?
This vitamin has both of the key mechanisms that scientists look for in anti-cancer compounds. In laboratory research, vitamin D has been shown to induce significant growth arrest of prostate cancer cells and to promote their death, which is called apoptosis. While no animal studies have shown complete cure of prostate cancer with vitamin D therapy, demonstrations of significant delay in cancer cell growth, delay in the progression of tumors, and prolonged survival in animals undergoing vitamin D treatment have all been completed and confirmed. This work has described the potential of vitamin D in prostate cancer therapy.
2. How common is vitamin D insufficiency, and who is most at risk?
Vitamin D insufficiency is most common at more northern latitudes, where people get less sun exposure. As you get farther away from the Equator—where sunlight
is most abundant—you are increasingly likely to have insufficient levels of vitamin D. Death rates from prostate cancer are also higher in northern latitudes.
In southern Europe, for example, vitamin D levels
are relatively high, and death rates from prostate cancer are relatively low in Mediterranean countries such as Greece and Portugal. But vitamin D levels steadily decrease and death rates from prostate cancer and other cancers steadily increase at higher geographic latitudes. In northern European countries such as Finland and Norway, vitamin D levels are considerably lower and prostate cancer death rates are considerably higher than they are in southern Europe.
Of course, a vitamin D level is not the only thing that distinguishes people in southern Europe from those in northern Europe. Thus, the association between regional prostate cancer variation and regional variation in vitamin D levels is not proof that vitamin D deficiency is the cause of increased prostate cancer risk—it’s more of a suggestion that requires further investigation.
In the United States, it’s estimated that 41 percent of men have inadequate levels
of vitamin D. Older adults are especially likely to have insufficient levels of vitamin D, partly because they spend less time outdoors, but also because aging skin cannot synthesize vitamin D as efficiently and aging kidneys are less able to convert the vitamin to its active hormone form.
Vitamin D insufficiency rates are highest among racial and ethnic minorities, especially among darker-skinned individuals who trace their ancestry to more southern latitudes. Darker skin, which has higher levels of melanin (a protective pigment whose major role is to absorb the ultraviolet light that comes from the sun), is less able than lighter skin to absorb vitamin D from sunlight, especially in northern latitudes where the sun’s rays are weaker.
It’s estimated that insufficiency levels are 81 percent among black men and 56 percent among Hispanic men.
Insufficiency levels may be even higher among immigrants from Asia, Africa, and the Middle East, who are more likely to follow Islamic dress codes that limit sun exposure. Researchers have noted that rickets (a bone disease associated with extreme vitamin D deficiency), which was practically eliminated from the United States after the introduction of vitamin D-fortified milk in the 1930s, has recently re-emerged in such immigrant populations.
3. What is the optimal blood level of vitamin D?
Vitamin D levels are assessed with a simple blood test that measures levels of 25(OH)D3, the metabolite that reflects vitamin D stores. Results are expressed in terms of nanograms per milliliter (ng/ mL). As noted before, average blood levels of vitamin D vary by geographical location as well as by age, race, and ethnicity. They also vary by season, with levels typically rising during the summer and falling during the winter.
Researchers define a vitamin D deficiency as a level below 17.8 ng/mL and a vitamin D insufficiency as 17.8–28 ng/ mL. They define an optimal level as 30 ng/mL or above, partly because it seems to be associated with a lower risk of all-cause mortality, and partly because it’s the established level that osteoporosis researchers consider optimal for maximal suppression of parathyroid hormone and reduced fracture rates.
Most experts recommend keeping your blood levels of vitamin D between 30 and 49 ng/mL.
4. How important is it for people to know their vitamin D status?
The take-home message from all this new vitamin D research is that vitamin D might be important for prostate health and is known to be important for many other aspects of health and well-being. Therefore, it’s very important to know your vitamin D status.
Endocrinologists have long assessed vitamin D status in patients who either have or are at risk for osteoporosis, and prescribed vitamin D supplements to help these patients achieve optimal levels. Only recently have doctors considered that it might be equally important to assess vitamin D status in patients at risk for cancer, cardiovascular disease, and infections. Unfortunately, most doctors don’t routinely measure vitamin D levels, so you will have to specifically request such a test.
During your next physical examination, ask your doctor to measure your vitamin D level along with other important markers of health such as cholesterol, triglycerides, and blood sugar levels.
If your level is optimal, it’s probably a sign that you’re getting enough vitamin D
from your diet, sunlight, or a combination of the two, and you don’t need to make any lifestyle changes. However, if your level is deficient or insufficient, it may be a sign that you need to start taking a vitamin-D specific supplement and having your blood levels regularly monitored. Standard multiple vitamins probably won’t work as well since they typically contain only 400 IU of vitamin D, an amount too low to raise blood levels into the optimal range.
5. How do doctors correct vitamin D deficiencies or insufficiencies?
This will vary from patient to patient. If you have a vitamin D deficiency, you may initially need to take a high-dose vitamin D supplement to raise your level into the optimal range; once you’ve achieved this, you can switch from the replacement dose to a maintenance dose. However, if you have a vitamin D insufficiency, you may only need to take a maintenance dose.
Most vitamin D supplements come in one of two forms: D2 and D3. They’re both effective, but D3 is preferred because it binds a little better to the vitamin D receptors. Alternatively, your doctor may prescribe a supplement that contains a combination of calcium and vitamin D. Over-the-counter vitamin D3 supplements contain 400 to 2,000 IU, while prescription supplements contain anywhere from 8,000 IU to 50,000 IU.
Most adults need at least 1,000 IU of vitamin D per day to achieve optimum blood levels. Older adults and darker-skinned individuals may need as much as 2,000 IU per day.
6. Is it possible to optimize vitamin D levels by consuming more D-rich foods?
You’re unlikely to get very much vitamin D from your diet unless you consume
large amounts of cod liver oil, which supplies 400 to 1,000 IU of D per teaspoon—but cod liver oil is no longer recommended as a dietary supplement because it may contain contaminants. In lieu of the oil, if you were to really focus on vitamin-D-rich foods, you might be able to obtain adequate levels of vitamin D, but supplementation is usually a more effective strategy.
Only a few commonly consumed foods are good sources of vitamin D3. One of the richest sources is salmon. Fresh wild salmon contains considerably more vitamin
D (600 to 1,000 IU) per 3.5-ounce serving than either fresh farmed salmon (100 to 250 IU) or canned salmon (300 to 600 IU).
Other good food sources of vitamin D include canned sardines, mackerel, and tuna, which contain 230 to 300 IU per 3.5-ounce serving. The vitamin is found in fortified milk and orange juice (about 100 IU per 8-ounce serving) and in fortified breakfast cereals (about 100 IU per serving).
Thanks to the milk-fortification program started in the 1930s to combat rickets, 99 percent of the U.S. milk supply is fortified with vitamin D. One cup of fortified milk provides 25 percent of the recommended daily intake for adults aged 51 to 70. For people 71 and older, it yields only 15 percent of the daily requirement. If you are between 19 and 50 years old, one cup of fortified milk will provide half of your recommended daily intake of vitamin D.
Smaller amounts of vitamin D are found in egg yolks (20 IU per yolk), liver (15 IU per 3.5-ounce serving), and Swiss cheese (12 IU per 1-ounce serving), but these foods also contain high amounts of cholesterol and saturated fat, which are associated with an increased risk of cardiovascular disease.
The (fat-free, cholesterol-free) shiitake mushroom contains an extraordinarily large amount of vitamin D2 (1,600 IU
per 3.5-ounce serving), but only in its sun-dried form.
A 3.5-ounce serving of fresh shiitake mushrooms contains only about 100 IU of D2, about the same as an 8-ounce glass of fortified milk.
7. Is it possible to optimize vitamin D levels by getting more sun exposure?
Sunlight is a major source of vitamin D. When the sun’s ultraviolet rays reach your skin, they convert the skin’s cholesterol precursors into vitamin D3. After vitamin D3 is transported to the liver, it undergoes a process called hydroxylation, which forms 25(OH)D, the metabolite that reflects vitamin D stores. After 25(OH)D is transported to the kidneys, it undergoes further hydroxylation that forms 1,25(OH)2D, which is vitamin D’s active metabolite.
One full-body exposure
to sunlight can give you 10,000 IU of vitamin D. Some experts say that you can achieve optimal vitamin D levels by occasionally foregoing sunscreen and exposing your face, arms, or legs to
10 to 15 minutes of sunlight two to three times a week.
However, this unreliable method depends on your geographical location, skin tone, and other variables. It might work year-round if you live in a sunny climate south of Nashville, Tenn., and have fair skin. However, if you live in the northern part of the United States—or if you have darker skin—it might be of limited value.
For example, if you’re
a resident of New Haven, Conn., you cannot get enough vitamin D from sunlight from November through February, regardless of your skin tone. That’s because
the sun’s rays are considerably weaker in northern latitudes during the winter. Furthermore, complete cloud cover reduces ultraviolet energy by half, and shade— which is enhanced by industrial pollution—reduces it by 60 percent.
It is very important for people who live in regions with limited sun exposure to include good sources of vitamin D in their diet. Although it’s unlikely that brief periods of unprotected sun exposure will cause skin cancer—especially if you alternate the exposed areas—the American Academy of Dermatology doesn’t recommend unprotected sun exposure as a means of getting adequate vitamin D. That’s because ultraviolet light is recognized as a carcinogen that increases the risk of skin cancer.
When leading endocrinologists treat vitamin D deficiencies or insufficiencies, they rely on supplementation. When carefully monitored, supplementation carries little risk of vitamin D toxicity and no risk of skin cancer.