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Did You Know That Most Cancers Can Be Linked To Nutrition Deficiency?
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Nutrition and Prostate Cancer
The purpose of this site is to provide an overview of literature
research that relates dietary intake to prostate cancer.
Follow the links below to find out how diet and prostate
cancer are linked, the key nutrients related to the development
and progression of prostate cancer, and ways that improvements
in nutritional intake may reduce one's risk of developing
prostate cancer, or limit its progression.
1. Evidence for Links Between Diet and
Prostate Cancer
2. Nutrients of Importance in Prostate Cancer and its
Prevention
3. Optimizing Nutritional Intake
4. References
5. Links to other information on the web
Evidence for Links Between Diet and Prostate Cancer
Many studies have shown that a person's risk of developing
prostate cancer is linked to where they live.
For example, a person in North America is much more likely
to develop prostate cancer than a person living in Asia.
However, the difference is not due to genetics, because,
within two generations, men of Asian descent living in North
America have the same prostate cancer risk as someone whose
ancestors have lived in North America for a much longer
period. While the exact reasons for the difference in prostate
cancer risk are not known, it is suspected that dietary
differences between the two regions may account for the
difference. Current knowledge of prostate cancer risk does
not provide definitive cause and effect relationships, but
evidence is being rapidly acquired, so that general guidelines
and approaches can be provided. Nonetheless, this is an
area of ongoing research, and these guidelines may evolve
as more information is acquired. Early studies (Willett,
1997;
Giovannucci, 1995) showed a strong positive correlation
between the incidence of prostate cancer and per capita
fat consumption in different countries. In addition, when
the diets of more than 50,000 health professionals were
analyzed, it was found that the men who ate the most fat
were almost twice as likely to develop prostate cancer as
men who had low fat diets (Health Professionals study, Giovannucci
et al., 1993). Similar studies aimed at looking at the role
of specific nutrients have suggested that deficiencies of
certain vitamins, such as vitamins D and E, may lead to
an increased risk of prostate cancer. These studies and
others suggest that there are ways that we can optimize
our dietary intake to reduce the risk of prostate cancer,
and to influence its progression.
Nutrients of Importance in Prostate
Cancer and its Prevention
Fat:
As previously noted, early studies suggested a strong link
between fat intake and risk of prostate cancer.
Although subsequent studies have not all been as conclusive,
the results generally show a positive relationship. In particular,
saturated fats are most strongly implicated. Although a
couple of studies have suggested that excessive intake of
animal fats, meats and dairy products may increase the risk
of prostate cancer, it is worth noting that these diets
are often also high in total fat and saturated fat (Clinton
and Giovannucci, 1998). It is therefore difficult to separate
these interrelated variables and to associate the risk directly
with any one of these food items. Nonetheless it would be
prudent to choose low fat or lean varieties of these foods.
It is worth noting that in the traditional North American
diet, approximately 40% of the calories come from fat. The
recommended intake is, in fact, that no more than 30% of
total calories come from fat. Clearly, for many people there
is an opportunity to modify their diets to reduce the fat
intake, and thus lower their risk of prostate cancer and
other diseases.
Vitamin D:
Vitamin D, along with calcium and phosphorus, are interacting
components within a complex network of nutritional and endocrine
pathways. The physiologically active form of vitamin D is
1,25 (OH)2-vitamin D. It is a highly regulated hormone,
and its concentration varies depending upon levels of calcium
and phosphate in the blood. For example, if the dietary
Intake of calcium is low, the blood level of 1,25 (OH)2-vitamin
D will increase, and vice versa. Thus, modification of vitamin
D intake must be considered in tandem with the intake of
calcium and phosphorus. Usually, as long as there is adequate
intake of vitamin D in the diet, the blood level of 1,25
(OH)2-vitamin D varies little (Clinton and Giovannucci,
1998).
Vitamin D has a clear role in prostate cancer prevention.
Epithelial cells in the prostate contain vitamin D receptors,
and 1,25 (OH)2-vitamin D has been shown to inhibit proliferation
of established prostate cancer cell lines (Miller et al.,
1995). Thus, a deficiency in vitamin D can lead to an increased
risk of prostate cancer. The Health Professionals Study
(Giovannucci et al., 1993) showed that the prostate cancer
risk was normal as long as dietary intake of vitamin D was
at or near recommended levels. There is no evidence in the
literature to suggest that intakes above the recommended
levels would reduce the risk of prostate cancer.
Vitamin E:
The role of vitamin E in prostate cancer has not been widely
studied. Low blood levels of vitamin E have been linked
to an increased risk of prostate cancer (Eichholzer et al.,
1996). However, one case-controlled study showed no relationship
between vitamin E and prostate cancer (Rohan et al., 1995),
and in another study of 29,000 Finnish smokers, daily consumption
of a 50 mg supplement of alpha tocopherol (a form of vitamin
E) reduced the incidence of prostate cancer and prostate
cancer deaths by 30 to 40% (Heinonen et al., 1998). The
question has been raised, however, as to whether these results
are applicable for non-smokers as well.
The recommended intake of vitamin E is 15
mg/day, an amount that is usually present in the typical
North American diet. Supplementation beyond these levels
should only be done after consultation with your Doctor
or Dietitian, because vitamin E can interact with some prescribed
medications. For most people, the safe upper limit for intake
is 1000 mg/day (ref: Food and Nutrition Board, U.S. Institute
of Medicine, April, 2000). Above 1000 mg/day, vitamin E
can have a pro-oxidant effect (i.e. it is no longer a protective
antioxidant).
Vitamin A and Beta-Carotene:
So far, there is no clear association between prostate cancer
risk and vitamin A intake. Some studies have indicated that
a deficiency leads to increased prostate cancer risk, while
others have suggested that vitamin A supplementation either
provides no protection or may lead to an increased risk
of prostate cancer (Kamat and Lamm, 1999). The source of
vitamin A may be important. In Asia, vitamin A is largely
obtained from vegetables, whereas in North America, the
main source of vitamin A is fat. Beta-carotene is a carotenoid
that can be metabolized to form vitamin A. Like vitamin
A, the link between beta-carotene intake and prostate cancer
risk is also unclear: intake of beta-carotene has been associated
with increased risk, decreased risk, or no effect on the
incidence of prostate cancer. A recent trial showed no benefit
from beta-carotene supplementation on the risk of prostate
cancer (ATBC study group, 1994).
Calcium:
Calcium intake in excess of 2000 mg/day has led to a three-fold
increase in the risk of prostate cancer, due to the fact
that increased dietary calcium reduces levels of (protective)
1,25 (OH)2-vitamin D (Health Professionals Study, Giovannucci
et al., 1993). Risk was independently increased by calcium
from both dairy and non-dairy sources, including supplements.
The literature does not, however, suggest any increased
risk at normal intake levels. Since adequate calcium is
necessary for bone health and the prevention of osteoporosis,
intake of 1000 - 1200 mg/day is recommended (ref: Food and
Nutrition Board, U.S. Institute of Medicine, Sept. 1999).
Lycopene:
Lycopene is a potent antioxidant, and is the major carotenoid
in tomatoes. Unlike other carotenoids (e.g., beta-carotene),
lycopene cannot be converted to vitamin A. Several epidemiological
and clinical trials have shown that diets rich in tomato
products and other lycopene-rich foods can reduce the risk
of prostate cancer (Giovannucci et al., 1995a and 1999;
Clinton et al., 1996). In addition, processed tomatoes contain
much more available lycopene than raw tomatoes. A 36% reduction
in risk was observed among men that consumed two or more
servings of tomato sauce per week, and in general, it has
been suggested that the greater the frequency of consumption
of tomato products, the greater the reduction in risk.
It is important to realize that approximately 18 different
forms of lycopene have been detected in prostate tissues
(Clinton et al., 1996), and furthermore, tomatoes contain
many other nutrients that may act together with lycopene.
Thus, it has not been conclusively determined that lycopene
alone mediates the relationship between prostate cancer
risk and the consumption of tomato products. At this time,
the best recommendation is to increase one's intake of processed
tomatoes (sauces, juice, etc.).
Selenium:
Selenium functions through selenoproteins, several of which
are oxidant defense enzymes. A strong association between
low selenium levels and increased risk of prostate cancer
has been reported (Willett et al., 1983). In another trial,
the risk of prostate cancer for men receiving 200 mcg of
selenium daily was one-third the risk of men receiving a
placebo (Yoshizawa et al., 1998). Nonetheless, further studies
are required to confirm these preliminary results.
Soy Products:
The consumption of soy-based products and related isoflavones
and phytoestrogens is much greater in Asian countries than
in North America, and this has been suggested as a possible
reason for the decreased risk of prostate cancer for Asian
men (Messina et al., 1994). In vitro, isoflavones have been
shown to inhibit the growth of androgen-dependent and androgen-independent
prostate cancer cells (Peterson and Barnes., 1993), although
the mechanism for these inhibitory actions is not known.
Further studies are required to better understand the role
of soy, isoflavones, and phytoestrogens in prostate cancer.
Given the preliminary evidence relating soy to prostate
cancer, it is worthwhile to consider increasing one's intake
of soy products. Although there is no guarantee of a direct
benefit, soy products are low in fat, and a reduction in
fat intake is much more clearly linked to a reduction in
prostate cancer risk.
Optimizing Nutritional Intake
Foods are complex nutrient packages, and contain many more
compounds than the vitamins and nutrients listed below.
Other compounds within the food may enhance the protective
effects of, for example, antioxidant nutrients, and the
carotenoids and isoflavones currently considered to be beneficial
may, in fact, simply point to other (as yet unidentified)
compounds that actually provide the protective effect.
There is clear evidence that a diet rich in fresh fruits
and vegetables reduces the risk of many diseases, including
cancer. The specific reasons and nutrients responsible for
this protective effect have not all been identified, and
are not completely understood. The protective effect is
likely related to complex interactions between constituent
phytochemicals that have not all been identified, let alone
incorporated into supplements. Thus, consumption of supplements
and food extracts may not provide the same benefits as fresh
fruits and vegetables. In essence, it is almost always better
to improve one's intake through food sources.
The first step towards improving nutrient intake is to understand
what you are currently consuming. A diet analysis based
on an accurate 5-day food intake or a food frequency questionnaire
is an excellent starting point. Based on the results, it
can be determined if you need to increase or reduce the
intake of certain nutrients within your diet. Based on recent
studies, you should pay attention to the following:
i) Reduce fat intake to no more than 30%
of total calories, and decrease intake of saturated fat
while increasing intake of omega 3 fatty acids
Many foods are sources of fat for the body. Fruits and vegetables
contain very small amounts of fats. Most of the fat in the
diet comes from added fat, such as margarine, oil, butter,
sauces, salad dressings, and gravies.
Meats, milk, and milk products can also provide a significant
amount of fat. Commercially prepared foods, such as cookies,
cakes, and doughnuts are another source of fat.
To reduce the amount of fat in the diet, choose lean and
lower fat foods and reduce the amount of fat added during
cooking and at the table. Consumption of lower fat milk
products, lean meats and alternates can greatly reduce the
total amount of fat in the diet.
Use lower fat cooking methods, such as baking, microwaving,
steaming, or broiling. Use nonstick pans to reduce the need
for oil during cooking.
To increase your intake of omega-3 fats (a "good"
polyunsaturated fat), consume salmon, trout, sardines, herring
or mackerel, flaxseeds and flax oil, walnuts, pumpkin seeds,
dark leafy vegetables, wheat germ, canola oil and soy products.
ii) Ensure that the recommended nutrient intake of vitamin
E is met.
vitamin E is found in foods containing fats, such as vegetable
oil, wheat germ, breads and cereals. It is most concentrated
in fats such as vegetable oil and margarine.
There is some evidence that supplementation may be beneficial,
but you MUST consult your physician before you consider
this, due to potential drug-nutrient interactions.
(iii) Ensure adequate intake of selenium
Good sources include cereal (though levels vary, depending
on the selenium content of the soil in which the cereal
grain is grown), meat, dairy and poultry. Fruits and vegetables
are poor sources of selenium.
There is some evidence that increased intake of selenium
may be beneficial, but you need to know how much selenium
is in your diet. Consult your physician and dietitian before
you consider supplementation, to ensure that your total
intake (food + supplement) does not reach unsafe levels.
iv) Increase your intake of soy products
Tofu, soy milk, soybeans and soy powders are examples
v) Ensure adequate intake of vitamin D and calcium
Excess calcium may increase the risk of prostate cancer,
and insufficient vitamin D may also increase one's risk
of developing prostate cancer.
Calcium is found in a variety of foods including dairy products
(milk, cheese, yogurt, and ice cream), legumes, nuts, salmon
(canned with bones), broccoli and almonds. Tofu made with
calcium can also be an important source.
Vitamin D is found in a limited number of foods, including
margarine, fish liver oils, milk, eggs, meat and fish.
vi) Ensure RNI levels of vitamin A are met
Vitamin A is found in foods such as eggs, liver, fish, fish
oils, fortified margarine, butter and milk.
Carotene (a vitamin A precursor) is found in dark green
and yellow vegetables, such as carrots, sweet potato and
tomatoes.
A deficiency of vitamin A may lead to an increased risk
of prostate cancer. There is no definite benefit from supplementation
of either vitamin A or beta carotene.
vii) Increase consumption of processed tomatoes and other
lycopene-rich foods
Processed tomatoes, tomato sauces and products are excellent
choices.
Other sources include pink grapefruit, watermelon, guava,
apricots, and papaya.
References
Alpha-tocopherol, beta-carotene cancer
prevention study group: The effect of vitamin E and beta
carotene on the incidence of lung cancer and other cancers
in male smokers. N. Engl. J. Med., 1994, 330, 1029-1035.
Clinton, SK and Giovannucci, E: Diet,
nutrition, and prostate cancer. Annu. Rev. Nutr., 1998,
18, 413-440.
Clinton, SK, Emenhiser, C, et al.: Cis-trans
lycopene isomers, carotenoids, and retinol in the human
prostate. Cancer Epidemiol. Biomarkers Prev., 1996, 5, 823-833.
Eichholzer M, Stahelin, HB, et al.: Prediction
of male cancer mortality by plasma levels of interacting
vitamins: 17 year follow-up of the prospective Basel study.
Int. J. Cancer, 1996, 66, 145.
Giovannucci, E, Rimm, EB, et al.: A prospective
study of dietary fat and risk of prostate cancer. J. Natl.
Cancer Inst., 1993, 85, 1571-1579.
Giovannucci, E: Epidemiological characteristics
of prostate cancer. Cancer, 1995, 75, 1766-1777.
Giovannucci, E, Ascherio, A, et al.: Intake
of carotenoids and retinol in relationship to risk of prostate
cancer. J. Natl. Cancer Inst., 1995a, 87, 1767-1776.
Giovannucci, E: Tomatoes, tomato-based
products, lycopene, and cancer: a review of the epidemiologic
literature. J. Natl. Cancer Inst. 1999, 91, 317-331.
Heinonen OP, Albanes D, et al.: Prostate
cancer and supplementation with a-tocopherol and b-carotene:
incidence and mortality in a controlled trial. J. Natl.
Cancer Inst., 1998, 90, 440 - 446
Kamat, AM, and Lamm, DL: Chemoprevention
of Urological Cancer. J. Urology, 1999, 161, 1748-1760.
Messina, MJ, Persky, V, et al.: Soy intake
and cancer risk: a review of the in vitro and in vivo data.
Nutr. Cancer, 1994, 1, 113-131.
Miller, GJ, Stapleton, GE, et al.: Vitamin
D receptor expression, 24-hydroxylase activity, and inhibition
of growth by 1-alpha,25-dihydroxyvitamin D3 in seven prostatic
carcinoma cell lines. Clin. Cancer Res., 1995, 1, 997-1003.
Peterson, G and Barnes, S: Genistein and
biochanin A inhibit the growth of human prostate cancer
cells but not epidermal growth factor receptor autophosphorylation.
Prostate, 1993, 22, 335-345.
Rohan, TE, Howe, GR, et al.:Dietary factors and risk of
prostate cancer: a case-control study in Ontario Canada.
Cancer Causes Control, 1995, 6, 145-154.
Willett, WC: Specific fatty acids and
risks of breast and prostate cancer: dietary intake. Am.
J. Clin. Nutr., 1997, 66, 1557-1563.
Willett, WC, Polk, BF, et al.: Prediagnostic
serum selenium and risk of cancer. Lancet, 1983, 2, 130-134.
Yoshizawa, K, Willett, WC, et al.: Study
of prediagnostic selenium level in toenails and the risk
of advanced prostate cancer. J. Natl. Cancer Inst., 1998,
90, 1219-1224.
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Links
1. Dietitians of Canada www.dietitians.ca
(analyze your nutrition profile, a mealplanner, healthy
body quiz, virtual kitchen, faq's and factsheets, find a
dietitian in your area list, nutrition events, nutrition
tip of the day, nutrition resources and more.)
2. Searchable recipe database: www.soar.Berkeley.EDU/recipes/
3. National Library of Medicine: www.nlm.nih.gov
4. National Institute of Nutrition: www.nin.ca
5. Health Canada On Line: www.hc-sc.gc.ca
6. Health Canada Nutrition On-Line Service: www.hcsc.gc.ca/main/hppb/nutrition/
"We would like to acknowledge the support of Sandra
Saville, RD of Saville Nutritional Consulting for her contribution
of this valuable nutritional information.
http://www.malehealth.com/
HTML/B5c2.html#nutrients
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