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Introduction
Considering the recent conflicting reports on caffeine - one
day it's OK to consume, the next day it's not - you may have had nagging doubts about the
health effects of your favorite caffeine-containing beverage.
Although people have consumed caffeinated foods and
beverages for hundreds of years, questions persist about its potential effects on women's
health. But according to leading medical and scientific experts, caffeine consumed in
moderation produces no adverse health effects.
From reproduction to osteoporosis, scientists worldwide have
investigated the effects of caffeine on women's health. This brochure provides background
information on caffeine and reviews the latest research on caffeine and women's health,
summarizing the major findings.
People have enjoyed caffeinated beverages since ancient
times. As long ago as 2,700 B.C. the Chinese Emperor Shen Nung sipped hot brewed tea.
Coffee's origins date back to 575 A.D. when in Africa beans were used as money and
consumed as food.
Caffeine is naturally occurring in the leaves, seeds or
fruits of more than 63 plant species worldwide. The most commonly known sources of
caffeine are coffee and cocoa beans, cola nuts and tea leaves. The amount of caffeine in
food products varies depending on the serving size, the type of product and preparation
method. With teas and coffees, the plant variety also affects caffeine content.
Various food consumption surveys show caffeine consumption
patterns have not changed significantly over the last decade. Caffeine consumption
averages around 200 mg. per day, and pregnant women tend to consume less caffeine than the
general population.
Physiological Effects
Depending on the amount consumed, caffeine can be a mild,
central nervous system stimulant. Since caffeine does not accumulate in the body over the
course of time, it is normally excreted within several hours of consumption. Any
pharmacological effects of caffeine are brief, usually passing within hours.
People differ greatly in their sensitivity to caffeine. With
regular use, tolerance develops to many of the effects of caffeine. For example, a person
who consumes caffeine on a regular basis may drink several cups of coffee in a few hours
and notice little effect, whereas a person who isn't a regular coffee drinker may feel
some stimulant effect after just one serving.
When regular caffeine consumption is abruptly stopped, some
people may experience symptoms, such as headaches, fatigue or drowsiness. These effects
usually are temporary, lasting for a few days, and often can be avoided if caffeine
cessation is gradual.
Overall, individuals tend to find their own acceptable level
of caffeine. Those who feel unwanted effects tend to ease off their caffeine consumption.
In practice, the person who experiences effects such as sleeplessness learns not to
consume caffeine before bedtime.
Caffeine and Pregnancy
- Is it Safe?
Today, with increased attention to maternal nutrition, many
women wonder if it's safe to consume caffeine-containing foods or beverages during
pregnancy. While some studies have shown conflicting results, the weight of scientific
research continues to indicate that moderate caffeine consumption does not affect
fertility, or cause adverse health effects in the mother or child.
Fertility
Since many women are delaying pregnancy, more research has
focused on identifying the factors that may affect fertility, including caffeine. One
small study in 1988 suggested that caffeine, equivalent to the amount consumed in 1- to
2-cups of coffee daily, might decrease female fertility. However, the researchers
acknowledged that delayed conception could be due to other factors they did not consider,
such as exercise, stress or other dietary habits. Since then, larger, well-designed
studies have failed to support these findings.
In 1990, researchers at the Centers for Disease Control and
Prevention and Harvard University examined the association between the length of time to
conceive and consumption of caffeinated beverages. The study involved more than 2,800
women who had recently given birth and 1,800 women with the medical diagnosis of primary
infertility. Each group was interviewed concerning caffeine consumption, medical history
and lifestyle habits. The researchers found that caffeine consumption had little or no
effect on the reported time to conceive in those women who had given birth. Caffeine
consumption also was not a risk factor for infertility.
Supporting those findings, a 1991 study of 11,000 Danish
women examined the relationship among number of months to conceive, cigarette smoking and
coffee and tea consumption. Although smokers who consumed eight or more cups of coffee per
day experienced delayed conception, nonsmokers did not, regardless of caffeine
consumption.
Miscarriages
The association between caffeine and miscarriages continues
to be researched. Recently, researchers from McGill University in Montreal published a
study showing a relationship between caffeine intake and miscarriage. While caffeine
intake before and during pregnancy appeared to be associated with increased fetal loss,
the authors failed to account for a number of factors that could result in a false
association, including effects of morning sickness or nausea, the number of cigarettes
smoked and amount of alcohol consumed.
Just prior to the McGill study, a research team from the
U.S. National Institute of Child Health and Human Development conducted a study of 431
women. The researchers monitored the women and the amount of caffeine they consumed from
conception to birth. After accounting for nausea, smoking, alcohol use and maternal age,
the researchers found no relationship between caffeine consumption of up to 300 mg per day
and adverse pregnancy outcomes, including miscarriage.
Additionally, in 1992, researchers analyzed the effects of
cigarettes, alcohol and coffee consumption on pregnancy outcome in more than 40,000
Canadian women. Although alcohol consumption and smoking tended to have adverse effects on
pregnancy outcome, moderate caffeine consumption was not associated with low birth weight
or miscarriages.
The Nausea Factor
For some women, nausea - "morning sickness" - is a
common experience during pregnancy. Though this phenomenon is unpleasant, researchers
believe it's a positve sign of a healthy pregnancy.
During a successful pregnancy, hormone levels are high, thus
increasing the likelihood of becoming nauseated. If you're nauseated, you're not likely to
consume all your favorite foods and beverages, including caffeine-containing beverages, so
you may resort to a diet of saltines and sips of water.
Because nausea affects what is consumed during pregnancy,
researchers usually account for this when studying the effects of certain foods and food
ingredients on pregnancy outcome. In the case of nausea's effects on caffeine consumption,
it appears that moderate caffeine consumption is an incidental, rather than a causative,
for miscarriages.
Birth Defects and Low Birth Weight
Studies published during the 1980s also support the
conclusion that moderate caffeine consumption during pregnancy does not cause early birth
or low birth-weight babies. A review of more than 20 studies conducted since 1980 found no
evidence that caffeine consumption at moderate levels has any discernible adverse effect
on pregnancy outcome.
A seven-year study of 1,500 women examined caffeine use
during pregnancy and subsequent child development. Caffeine consumption, equivalent to
about 1 1/2 - 2 cups of coffee per day had no effect on birth weight, birth length or head
circumference. Follow-up examinations at ages eight months, four and seven years also
revealed no effects of caffeine consumption on a child's motor development or
intelligence.
In the early 1980s, the U.S. Food and Drug Administration
(FDA) conducted a study where rats were force-fed very high doses of caffeine through a
stomach tube. While the results prompted an advisory to pregnant women to avoid caffeine,
the study was criticized as not being representative of the way humans consume caffeine.
In 1986, FDA researchers carried out another study, in which
rats consumed high doses of caffeine in their drinking water. At the conclusion of the
second study, the FDA found no adverse effects in the offspring, contradicting the
agency's earlier findings.
Major studies over the last decade have shown no association
between birth defects and caffeine consumption. Even offspring of the heaviest coffee
drinkers were not found to be at higher risk of birth defects. FDA has evaluated this
scientific evidence and concluded that caffeine does not adversely affect reproduction in
humans. However, as with other dietary habits, the agency continues to advise pregnant
women to consume caffeine in moderation.
But remember, drinking plenty of fluids, preferably water,
is important during pregnancy. Though consuming moderate amounts of caffeine is fine,
health professionals also remind pregnant women to drink a variety of beverages daily.
Breast Feeding
Women should also take note of what they eat while breast
feeding to ensure healthy milk production. Though caffeine can permeate into breast milk,
nursing mothers can safely consume up to 300 mg of caffeine (2-3 cups of coffee or several
cans of cola) without passing on a significant amount of caffeine to the baby.
The American Academy of Pediatrics Committee on Drugs has
reviewed the effects of caffeine on breast feeding and reported that moderate caffeine
consumption has no effect on breast feeding. As with all foods, pregnant and lactating
women should apply the principle of moderation to caffeine and discuss it with their
personal physician or health care provider. A reasonable guideline is around 300 mg daily.
Fibrocystic Breast Disease
Caffeine was first discussed in relation to breast disease
in the late 1970s. An informal study suggested that abstinence of caffeine might alleviate
the symptoms of fibrocystic breast disease, a condition of benign fibrous lumps in the
breast. Though caffeine was not linked to development of the disease, some subjects
reported feeling less breast tenderness when they eliminated caffeine from their diets.
However, the findings were based on anecdotal reports from a small number of women, rather
than clinical testing, making the conclusions unreliable.
A larger study conducted by the National Cancer Institute
(NCI) involved more than 3,000 women. This 1986 study showed no evidence of an association
between caffeine intake and benign tumors, fibrocystic breast disease or breast
tenderness.
Both the NCI and the American Medical Association's (AMA)
Council on Scientific Affairs have stated there is no association between caffeine intake
and fibrocystic breast disease.
The Cancer Question
The concern raised about caffeine and fibrocystic breast
disease led to a concern about possible association between caffeine consumption and
breast cancer. However, extensive research conducted to date has shown no association
between caffeine consumption and the development of any cancer.
Breast Cancer
In 1990 researchers reviewed scientific data investigating
caffeine and malignant breast tumors. Out of 11 studies reviewed, none established a
significant link between caffeine intake and breast cancer incidence.
Specifically, three separate studies performed in Israel,
the United States and France, analyzed the relationship of coffee consumption to breast
cancer development. Each study respectively accounted for dietary intake, medical and
reproductive history and frequency of coffee intake. The results of each investigation
established no association between coffee consumption and breast cancer.
Furthermore, the 1986 NCI study on breast disease found no
association between caffeine consumption and breast cancer. Interestingly, the NCI
researchers noted that coffee drinkers had a slightly lower incidence of breast cancer.
Preliminary findings from the Harvard Nurses' Health Study also showed that women who
consumed the highest amount of caffeine had a lower risk for breast cancer.
Ovarian Cancer
In a thorough review of the research on caffeine's
relationship to ovarian cancer, no evidence indicated that caffeine consumption is a risk
factor for ovarian cancer when known factors are taken into account. In fact, the
International Agency for Research on Cancer (IARC) found there is inadequate evidence to
suggest coffee drinking causes ovarian cancer.
Overall, the universal scientific research does not support
a relationship between caffeine consumption and cancer. As a result, both the American
Cancer Society and the National Academy of Sciences' National Research Council report
there is no convincing evidence relating caffeine to any type of cancer .
Osteoporosis - Boning up on Health
Given the recent awareness about the incidence of
osteoporosis in post-menopausal women, the relationship between caffeine and bone health
is a relatively new area of investigation. Because caffeine intake often causes an
increase in calcium loss, it has been suggested as a risk factor for osteoporosis. Yet
studies show that adequate calcium consumption offsets the potential effect of caffeine on
bone density.
This is illustrated in a recent study that examined the
lifetime intake of caffeinated coffee in 980 postmenopausal women. The researchers found
no association between lifetime caffeinated coffee intake (equivalent to two cups per day)
and reduced bone mineral density among women who drank at least one cup of milk a day
during their adult lives.
Other studies conducted at The Pennsylvania State
University's College of Medicine and the Mayo Clinic have found that while caffeine intake
slightly increases urinary calcium excretion, caffeine was not an important risk factor
for osteoporosis.
Given the current evidence, an adequate calcium intake -
especially during adolescent years - is the best nutritional insurance for healthy and
strong bones. Women of child bearing age should eat at least three servings a day of
calcium-rich foods, such as low-fat milk or yogurt.
Caffeine and Heart Disease - Matters of the Heart
Caffeine and heart disease is another area that has been
extensively examined, and no causal relationship between caffeine consumption and heart
disease, high blood pressure or irregular heart beat has been shown.
While most studies investigating heart disease in large
populations involve men, two studies have included women. Researchers of the recent
Scottish Heart Health Study conducted a study of 10,359 men and women aged 40-59. Their
analysis showed no relationship between coffee consumption and heart disease; in fact,
they found that coffee may actually protect against heart disease.
Additionally, the well-respected Framingham Study analyzed
the relationship between coffee consumption and incidence of heart disease in 2,648 men
and 3,566 women. After examining all possible links between coffee intake and heart
disease, the researchers reported that no harmful effect of coffee consumption was found
and that there was no association between coffee intake and recurring heart attack
episodes.
The effects of caffeine on blood pressure and irregular
heart beat have also been topics of scientific investigation. The American Medical
Association's Council on Scientific Affairs concluded that abstaining from caffeine did
not significantly influence the occurrence or frequency of irregular heart beat. Likewise,
the U.S. Surgeon General's report Nutrition and Health states a number of studies have
shown that any rise in blood pressure due to caffeine consumption is less than the
elevation produced by normal, daily activities, such as climbing stairs.
What Next?
As long as there are questions regarding the safety of food
and food ingredients, researchers will continue to look for answers and, indeed, there are
many studies in progress. Yet there is no shortage of research on the health effects of
caffeine. The overwhelming scientific evidence on this ingredient shows that moderate
caffeine consumption is safe.
This article is reprinted with permission from the International Food Information Council
Foundation, September 1998.
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