Nutrition Myths
Is caffeine bad for you?


  • The positive or negative health effects of caffeine mainly depend on the individual’s genetic predisposition.
  • Caffeine is good for fast caffeine metabolizers which represent the majority of the population.  For this group, 400-500mg of caffeine daily provides the maximum health benefits and the minimum negative side-effects.
  • Caffeine can be bad for you, if you are a slow caffeine metabolizer, are allergic to caffeine, overdose on caffeine, reached the caffeinism stage, are pregnant, are in the risk group of developing breast cancer or if you suffer from indigestion (GERD).


Is caffeine bad for you?

Since there is no definitive answer to the question of whether caffeine is bad or good for you, you should read the following and assess what scenario applies to your case.

Caffeine levels in drinks and food

Caffeine is a naturally occurring substance in fruits and the leaves of plants such as coffee, tea, yerba mate and guarana. It is present in many products including sodas, energy drinks, chocolate bars, cough syrups and slimming tablets.

Caffeine is also added to some over-the-counter medicines such as cold medications. Caffeine contents in drinks and foods may range anywhere from trace amounts in decaffeinated drinks such as coffee or tea to over 300mg per serving in products such as energy drinks or Starbucks coffee.

For the full list of contents of caffeine in drinks please see “Caffeine levels in drinks and foods”

Is caffeine a drug?

Caffeine is a stimulant drug (known as a psychoactive drug) that affects the nervous system, causing symptoms such as alertness and temporary mood elevation.

It also affects the rest of the body such as the hormonal system and the metabolism of fat during exercise (although studies showing long term weight-loss effects are inconclusive). (1)

Caffeine is a dose-dependent drug. The larger the dose, the stronger the stimulation effects. However, it doesn’t collect in the body, but gets broken down in the liver and excreted through urine. (2)

Caffeine reaches the bloodstream in about 15 minutes, attaining its peak saturation in the blood in 15-45 minutes. It has a half-life of around 6 hours (the time taken for the caffeine concentration in your blood to reduce by half). (3)

Although a drug, caffeine is not addictive like other drugs. Nevertheless, individuals who drink caffeine daily develop a physical dependence to it. (read more..)

How does caffeine affect your body if you are allergic, sensitive or caffeine-naive?

The way you handle caffeine and the intensity of the symptoms depend on a variety of factors, such as the individual’s sensitivity and tolerance level to caffeine, and in rare cases caffeine allergy.

In other words, the positive and/or negative effects that caffeine exerts on each person and if one should drink caffeinated drinks and in what quantities are closely correlated to:

  • Caffeine allergy

    Caffeine allergy is extremely rare, with only a handful of cases recorded. However, if you show common allergic reactions to caffeine such as hives or anaphylaxis, you should avoid any amount of caffeine. (read more..)

  • Caffeine sensitivity

    The bottom line is, are you a fast or a slow caffeine metabolizer?

    Caffeine sensitivity is an important factor that determines whether coffee is good or bad for you. The genetic make-up dictates how many caffeine-breaking enzymes are produced by the body, therefore influencing how well you can handle caffeine.

    Being caffeine-sensitive or a slow caffeine metabolizer restricts how much coffee you can manage, by producing unpleasant overdose symptoms as soon as you surpass your caffeine limit.

    Negative rather than positive health effects are likely to occur as a result of caffeine intake. The more caffeine sensitive you are, the less caffeine you are able to consume before you experience the negative effects. In extreme cases, if you are very sensitive, you may not be capable of having any caffeinated drinks. (read more..)

    Fast caffeine metabolizers, on the other hand, can quickly break down and excrete caffeine. They normally experience a wide range of health benefits of caffeine intake, as mentioned in the section below.

    The main point is that, if you are sensitive to caffeine, drinking caffeinated beverages will bring you more negative than positive effects, depending on the sensitivity level and on the amount consumed. However, if you are a fast metabolizer, the positive effects of caffeine intake described below may be applicable.

    NOTE: many studies on caffeine don’t take into consideration genetic factors.

    You are not sensitive to caffeine. In this case, you may build your tolerance to the point of over-consumption and high dependency (caffeinism), which has detrimental results on your health. Studies don’t show any health benefits from such high amounts of caffeine.

    NOTE: many studies don’t take into consideration the tolerance factor, making the results misleading. For instance, we cannot conclude that energy drinks’ containing caffeine, have a diuretic effect if we don’t know if the participants are usual consumers of caffeinated drinks. Their increased urination may be due to the fact that they haven’t developed a tolerance to caffeine rather than caffeine having a diuretic effect.

Negative effects of caffeine

Negative health consequences (often leading to serious medical conditions) are associated with caffeinism, high sensitivity, overdose or allergy to caffeine as described in the section above. Learn your limits of caffeine intake to avoid potentially dangerous outcomes.

  • Caffeine and GERD (gastroesophageal reflux disease)

    In people who suffer from GERD, or peptic ulcer, caffeinated coffee has shown to worsen these conditions more significantly than decaffeinated coffee. It is advisable for GERD sufferers to avoid caffeinated drinks, especially coffee. (4, 5, 6)

  • Caffeine and blood pressure

    Caffeine raises blood pressure when the tolerance to caffeine is not complete. If caffeine is taken after a period of abstinence, individuals experience a slight rise in blood pressure. However, this increase in blood pressure is reduced or totally disappears with continuous caffeine intake of the same dosage.

    For individuals with a moderate to high caffeine intake, half of them will build tolerance to caffeine within 5 days and their blood pressure will return to normal. The other half, on the other hand, will continue with slightly elevated blood pressure, even if they are used to consume a moderate to high amount of caffeine daily.

    The increase in blood pressure is small, of about around 3mm Hg. Nevertheless, these changes may negatively affect individuals at high risk of cardiovascular diseases.

    Regular caffeine intake by people prone to hypertension may be harmful and is not advisable.

    The effects of caffeine on the cardiovascular system is thought to be due to the blocking of adenosine receptors and the inhibition of phosphodiesterases. (7, 8)

  • Caffeine and heart health

    Studies show quite different health effects of caffeine on the heart health depending on if you are a slow or a fast metabolizer.

    Slow metabolizers have an increased risk of non-fatal heart attack, if they drink 2-3 cups of coffee daily (200-300mg caffeine). Additionally, those who drink 4 cups of coffee per day have a four time greater chance of having a heart attack compared with those who drink about one cup (100mg caffeine) per day. (read more..)

    For fast metabolizers, on the other hand, caffeine improves heart health and reduces the risk of heart attack. See the section for the health benefits of caffeine below.

  • Caffeine and anxiety

    Dependence on caffeine, having an overdose of caffeine or stopping caffeine intake after long term use may induce symptoms of anxiety. (9)

  • Caffeine and dehydration

    Caffeine as a drug has diuretic properties. When taken in high amounts, especially in a tablet form (not as a caffeinated drink), it causes the kidneys to increase the production of urine. High doses of more than 360mg of caffeine increase urine production. (10)

    However, when taken as coffee, tea, or other caffeinated drinks, such as soda or energy drinks, the contribution of the liquid negates the diuretic effects of caffeine. Caffeinated drinks can, therefore, be considered as being hydrating.

    For most individuals, the diuretic effects of caffeine get reduced or completely disappear with the increased tolerance to caffeine (within 1-5 days). This means that after a period of caffeine abstinence, a dose of caffeine may cause various effects on the body, including increased urination, but after becoming accustomed to the regular caffeine intake, these symptoms disappear. (Read more..) (11)

    If caffeine is consumed before exercise, its’ diuretic properties  are negated compared to having caffeine followed by rest.

    Please be aware that some studies that have shown the diuretic effects of energy drinks didn’t take into account the caffeine tolerance factor and, therefore, are flawed.

    In summary:

    1. consuming caffeine without liquid may cause more urination;
    2. regular caffeine users have minimal or no effect on urination;
    3. caffeine before exercise doesn’t cause increased urination;
    4. you may urinate more after a caffeinated drink if you are already well hydrated.
  • Caffeine and sleep (especially if consumed in the afternoon)

    Caffeine can affect sleep quality. Around 90% of the adult population in United States consumes caffeine in the afternoon (between noon and 6pm), and 68.5% in the evening (6pm-midnight). On average, adults consume about 329 mg (+- 180mg) of caffeine per day.

    Generally, for moderate caffeine users (400mg of caffeine/day) the sleep disturbances (poor sleep quality, reduced sleep time, time taken to fall asleep and sleep efficiency) occur with a dosage consumed up to 6 hours before sleep time.

    Therefore, it is recommended to abstain from caffeinated drinks for a minimum of 6 hours before sleep time (on average, it should be avoided after 5pm). (12, 13)

  • Caffeine intake may increase the risk of infertility and miscarriage

    Overall, current guidelines recommend limiting caffeine consumption to a maximum of 200mg daily (e.g. 2 coffees). (14) However, it may vary between individuals and in some cases 200mg per day may be too much.

    Caffeine rapidly crosses the human placenta and reaches a similar concentration in the fetus. (15)

    If you are a slow metabolizer and consume 2-3 coffees per day, the risk of infertility and miscarriage increases. (16) An increase of 100mg of caffeine intake per day (equivalent to 1 cup of coffee) is associated with a 7% higher risk of loss of pregnancy (16), and a 13% higher risk of a lower birth rate. (17)

    One study showed that an amount of caffeine below 300 mg per day (around 1-2 coffees or 4 cups of tea) doesn’t increase the risk of spontaneous abortion or pregnancy complications, reduce fertility, or have an adverse neurodevelopmental effect.

    However, this study doesn’t take into account the caffeine sensitivity aspect, which means that its results may be not applicable to slow metabolizers.

    Studies on infertility show that large amounts of caffeine may increase the risk of infertility. Small amounts of caffeine, however, have no impact. Therefore, when planning to get pregnant is recommended decrease the caffeine intaketo no more than 300mg per day. (18, 19)

  • Caffeine and Fibrocystic Breast Disease

    Caffeine consumption has been associated with a higher risk of fibrocystic breast disease in women. The association was the highest in women who had a higher risk of developing breast cancer.

    Daily caffeine amounts of between 31 and 250 mg increase the risk by 1.5 times and amounts over 500 mg by 2.3 times. (20)

  • Caffeine and indigestion

    Caffeine intake by obese individuals is associated with indigestion. (21)

  • Caffeine and insulin sensitivity

    Caffeine consumption can decrease glucose uptake and insulin sensitivity. (22, 23)

  • Caffeine and menopause

    Caffeine use is associated with greater vasomotor symptom bother (e.g. hot flashes and night sweats) in postmenopausal women. (24)

  • Caffeine and seizure disorders

    Caffeine supplements may lower the seizure threshold in individuals with seizure disorders which means that it may induce new seizure occurrences. (14)

  • Caffeine medication contraindications

    Caffeine increases the activity of a so called hepatic cytochrome P450 (CYP)1A2.  It can be thought of as a group of enzymes that break down not only caffeine or alcohol but also various medications. This means that an increased activity of CYP1A2 may impact the potency of some medications.

    Other medications may reduce the activity of CYP1A2 and, therefore, reduce the break-down and elimination of caffeine, causing adverse health effects from an excess of caffeine. (25, 26)

    Consult your doctor about the amount of caffeine you should be consuming daily when on medication.

The caffeine intake may additionally lead to:

  • Caffeine overdose

    You can have a caffeine overdose, regardless of whether you are sensitive to caffeine or not. This depends on the combination of the caffeine dose and your level of sensitivity.

    You can be extremely sensitive to caffeine and a few sips can be enough to cause the onset of symptoms or you can handle caffeine very well and 5 coffee shots in one go might not affect you. To avoid caffeine overdose, learn your safe limit.

Health benefits of caffeine – when is caffeine good for you?

Most of the caffeine health benefits are experienced by people who are not allergic or sensitive to caffeine and don’t consume excessive amounts or overdose on caffeine.

  • Caffeine and cognitive function and psycho-motor performance

    Caffeinated beverages, such as coffee or tea, if consumed throughout the day, improve alertness, learning capacity, mood, memory and psychomotor performance. These results refer to medium to high caffeine users, rather to low caffeine users.

    Please note that low caffeine users may be sensitive to it and, therefore, be affected negatively by caffeine intake through anxiety, jitteriness and reduced quality of sleep. (27, 28)

  • Caffeine and weight loss

    Caffeine exerts some weight reducing effects in the short term, by increasing the rate of burning fat and boosting the metabolic rate.

    However, in the long term, these effects are negligible due to the increased tolerance to caffeine. Nevertheless, it may be positive as a tablet or powder when taken before exercise to help increase the burning of the fatty tissue. (read more..)

  • Caffeine and Gout

    Long term caffeine consumption is associated with decreased risk of gout. (29)

  • Caffeine and heart health

    As explained above, there are distinct health effects of caffeine on heart health depending if you are a slow or fast metabolizer. Heart health benefits of caffeine only apply to fast metabolizers.

    For medium to high caffeine users, those that can handle larger amounts of caffeine, or fast metabolizers, long term caffeine intake, of about 400mg of caffeine (between 3-5 cups of coffee daily), shows the largest reduction on cardiovascular disease risk. For this group, there is a 22% lower risk of heart attack by having 200-300mg caffeine per day (2-3 cups of coffee).

    The risk doesn’t increase even with larger amounts of coffee. (30, 31)

    To see the effects of caffeine on slow metabolizers, please see the above section listing negative effects.

  • Caffeine and skin cancer

    Two recent, large studies on the effects of coffee on skin cancer have found that caffeinated coffee consumption is associated with a reduction of a risk of malignant melanoma by up to 25%.

    Because decaffeinated coffee didn’t show a significant association with the risk of melanoma, scientists think that this may be due to caffeine. More studies on caffeine are planned to confirm these theories. (32, 33)

  • Caffeine and depression

    Several observational studies show that higher caffeine users (especially in coffee) have a decreased risk of depression and depression related suicides. An amount of caffeine of about 400mg (equivalent to 4-5 coffees) is the most optimal in risk reduction and is associated with 20% lower risk of developing depression and 53% lower suicide risk.

    However, the risk increases with a usage of 800mg of caffeine per day or more (at least 8 cups of coffee per day) (34, 35, 36, 37).

  • Caffeine and Alzheimer’s Disease

    Caffeine consumption has been shown to reduce the risk of developing Alzheimer’s disease. (38, 39, 40)

  • Caffeine and Parkinson’s

    Caffeinated coffee drinkers have a 31% decreased risk of developing Parkinson’ disease. (41, 42, 43, 44)

  • Caffeine and dementia

    Caffeine intake reduces the risk of developing dementia. Scientists believed that factors responsible for this reduction may be due to caffeine, antioxidant capacity and increase of insulin sensitivity. (45, 46)

  • Caffeine and multiple sclerosis (MS)

    Studies on the association of caffeine and MS are still inconclusive. Some observational studies show no association, while the most recent study, from 2016, found a correlation between high consumption of caffeinated coffee and about 30% of decreased risk of multiple sclerosis.

    This is thought to be due to the caffeine’s neuroprotective properties, and its ability to suppress pro-inflammatory cytokine production. More studies are needed, however, to confirm these findings of caffeine involvement. (47)

  • Caffeine and physical performance of the athletes

    Caffeine (specifically as a capsule/tablet or powder) when taken before exercise, is effective in increasing physical performance (especially in high-intensity workouts of prolonged duration).

    It improves performance by acting on several areas in the body: it increases focus and alertness, boosts energy, causes a higher release of epinephrine (adrenaline), increases the release of body fat for energy usage and aids in burning more fatty acids during exercise.

    For optimal absorption, it is advisable to take the supplement 60 minutes before the exercise. However, it is also effective when taken 15-30 minutes before exercise. Studies are inconsistent on the effectiveness of caffeine in strength-power exercises. (48, 49)

  • Caffeine and Diabetes 2

    Habitual caffeine consumption may reduce the risk of diabetes mellitus. (50, 51, 52, 53)

  • Caffeine and liver (cirrhosis)

    Caffeine in synergy with other compounds present in coffee may have protective properties against alcoholic and non-alcoholic cirrhosis, and reduce the mortality risk from cirrhosis. (54, 55, 56)

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