From the FDA’s own web page:

For healthy adults, the FDA has cited 400 milligrams a day—that’s about four or five cups of coffee—as an amount not generally associated with dangerous, negative effects. However, there is wide variation in both how sensitive people are to the effects of caffeine and how fast they metabolize it (break it down).

Certain conditions tend to make people more sensitive to caffeine’s effects, as can some medications. In addition, if you’re pregnant, trying to become pregnant, or breastfeeding, or are concerned about another condition or medication, we recommend talking to your health care provider about whether you need to limit caffeine consumption.

The FDA has not set a level for children, but the American Academy of Pediatrics discourages the consumption of caffeine and other stimulants by children and adolescents.

Spilling the Beans: How Much Caffeine is Too Much? | FDA

The FDA has anchored the “400 mg” into public consciousness.

Problem #1 is that most of us have absolutely no idea how much caffeine we are consuming. How much caffeine is in a “cup” of coffee depends on cup size, the type of bean used, and the method of brewing. This can easily be up to 4x difference in caffeine content from 60 to 250 mg or more per “cup”.

In caffeine health studies, they define a cup as “6 ounces”. But not one person still drinks coffee in a 6 oz cup. Today, coffee is supersized into 12, 16 or 21 oz paper cups or 14-18 oz “mugs”.

Many other food products (especially sodas and other beverages) contained intentionally added caffeine. This can amount to hundreds of milligrams. And some of those drinks come with free refills …

Problem #2 is the general meme that coffee is fine for almost everyone.

Studies find that up to half of us are “caffeine sensitive”. That means we metabolize caffeine slowly so that caffeine remains in our body for longer, sometimes much, much longer. That in turn means if we have a 2nd “cup” a few hours later, we are piling on the caffeine as it is cumulative with the caffeine from cup #1 still circulating in our bodies.

The FDA/public health does not give clear directions on how to determine if you are caffeine sensitive. Instead, the FDA and nearly everything in our society, promotes daily coffee consumption as healthful burst of energy.

I recently discovered the hard way that I am highly caffeine sensitive – yet had been consuming coffee – typically 1 to 2 “cups” per day for about 20 years. In fact, coffee was likely to kill me.

For then unknown reasons, my blood pressure would spike super high at times. How high? How about 160 to 200 over 90 to 120. At which point, this was life threatening.

The connection to coffee consumption was not obvious. The BP spikes, in turn, were leading to visual migraines, with significant migraines occurring every other day, and minor ones every day.

I thought I drank 1-2 cups of coffee per day – the FDA said that was not a problem. After discovering these problems connected to coffee, I determined that the beans and how I made my coffee was likely yielding 200-500 mg of caffeine per day, far above the “around 100 mg” I thought I was having.

I’d kept a log for the past two years of BP and migraines – and doing some simple data analysis spotted a pattern. One of my charts plotted the visual aura start time by hour of the day – for each of the days I had one or more visual migraines occur in 2022. Immediately I saw that almost all auras started between 8 and 2 pm. I immediately thought of coffee.

13 days ago I ended coffee consumption, not even having decaf. I am still in the “caffeine withdrawal” phase, which is very tough – causing its own headaches, fatigue, and both sleepiness at times and insomnia at other times. The Expert say this lasts 2-9 days, but as usual, The Experts are wrong – many, many, many firsthand reports say 2-4 weeks of withdrawal is not uncommon.

What’s already happened?

  • My blood pressure is now normal every day – with readings like 105-115/73.
  • My resting pulse is typically about 63 with a range of 57-67. Lying down this morning, my resting pulse was 51. Compare to 76-82 commonly measured while high on coffee.
  • My heart rate recovery after exercise is now normal, with a 20% drop in 5 minutes, and a steady drop continuing after that. Previously, my heart rate recovery left my heart running fast for up to 1-2 hours. No more.
  • I have had only 2 minor visual disturbances (visual migraines or auras) since dropping coffee, and one of those was on day #2 – and was subdued. This is a decrease from experiencing visual disturbances every day up to the day I quit.

I also reviewed a past DNA traits analysis done as part of a family history genetic/DNA evaluation. It had marked me as “high evidence” for “high caffeine sensitivty”. I have almost all of the genetic markers for caffeine sensitivity.

Obviously, I need to keep records on this progress over a much longer period of time – probably 1-3 months – to know how this turns out long term. At this point, I do not see myself going back to caffeinated beverages.