The authors explained that about 80% of caffeine consumption worldwide is in the form of coffee - it is the most commonly used CNS (central nervous system) stimulant.
Previous studies have looked at associations between coffee drinking and depression risk - one prospective study among young adult males suggested coffee consumption might be linked to depression risk. Depression is often a long-term (chronic) condition that has a tendency to come back, it affects twice as many females as males. Experts say that about 1 in every 5 women in the United States will suffer from depression at some point in their lives.
The authors wrote that:
"(the) identification of risk factors for depression among women and the development of new preventive strategies are, therefore, a public health priority."
Michel Lucas, Ph.D., R.D. and team set out to determine whether the consumption of coffee or some drinks containing caffeine might be linked to depression risk.
They gathered data on 50,737 women, average age 63 years; none of them had depression when the study began. They had all participated in the Nurses' Health Study. They were prospectively followed up until June 2006. Questionnaires had asked them what their caffeine consumption was from 1980 to 2004. The researchers had data on how often they consumed caffeinated and non-caffeinated coffee, nonherbal tea, caffeinated sodas (sugared or low calorie), all types of caffeine-free soft drinks, and chocolate during a twelve month period before filling in each questionnaire.
In this study, depression was defined as having a diagnosis of clinical depression and being prescribed regular antidepressants during the previous two years.
They analyzed the cumulative consumption over a period and then looked at a two-year latency period. For example, caffeine consumption data from 1980 through 1994 were used to predict clinical depression rates from 1996 through 1998.
They identified 2,607 new diagnoses of depression during the 10-year follow up period 1996-2006.
Below are some highlighted data from their findings:
- Women who consumed two to three cups of caffeinated coffee per day were 15% less likely to develop depression compared to those who drank a maximum of one cup of caffeinated coffee per week
- Women who drank at least 4 cups per day had a 20% lower risk than the maximum 1 cup per week females
- Those who consumed at least 550mg per day of caffeine had a 20% lower risk of developing depression compared to the women whose daily consumption was 100mg or less per day
- The consumption of decaffeinated coffee had no impact on depression risk
"In this large prospective cohort of older women free of clinical depression or severe depressive symptoms at baseline, risk of depression decreased in a dose-dependent manner with increasing consumption of caffeinated coffee."
"(this observational study) cannot prove that caffeine or caffeinated coffee reduces the risk of depression but only suggests the possibility of such a protective effect."
Further studies are required to confirm their findings, as well as to determine what impact regular caffeine consumption might have on the general population, and whether it could be used to treat depression.
Caffeine content in some food, drinks and drugs
- Caffeine tablet (regular strength), 1 tablet. 100 mg
- Caffeine tablet (extra strength), 1 tablet. 200 mg
- Excedrin tablet, 1 tablet. 65 mg
- Hershey's Special Dark (45% cacao), 1 bar of 1.5 oz. 10 mg
- Percolated coffee, 7 fl oz. 80-135 mg
- Drip coffee, 7 fl oz. 115-175 mg
- Decaffeinated coffee, 7 fl oz. 5-15 mg
- Espresso coffee, 1.5-2 fl oz., 100 mg
- Black tea, 6 fl oz. 50 mg
- Green tea, 6 fl oz. 30 mg
- Guayaki yerba mate, 0.2 oz. 85 mg
- Coca-Cola Classic, 12 fl oz. 34 mg
- Mountain Dew, 12 fl oz. 54 mg
- Gurana Antartica, 11 fl oz. 30 mg
- Jolt Cola, 23.5 fl oz. 280 mg
- Red Bull, 8.2 fl oz. 80 mg (Source: Nutrition Action)
Caffeine's effect on some animalsMost humans can drink caffeine relatively safely. However, it is very toxic to some animals, such as birds and dogs. Caffeine can have some weird effects on spiders, as can be seen in the picture below.
The spider on caffeine makes a pretty useless web