Coffee – Good or Bad for your Brain?

by Patrick Holford

Coffee: Friend or Foe for Your Brain?

For many, the day doesn’t truly begin until that first cup of coffee hits the system. It sharpens the mind, lifts the fog, and gives an instant boost of focus – which explains why, in the UK alone, we drink an astonishing 100 million cups every single day, about two per person. But is this daily ritual really fuelling your brain, or quietly robbing it of long-term vitality?

Coffee is more than just a stimulant. Yes, it contains polyphenols – those antioxidant compounds that can protect the brain. But it also delivers caffeine, which fires up your adrenal hormones to give that short-term buzz. The problem is that this instant lift comes with a hidden cost: over time, it can deplete energy reserves and, more worryingly, raise homocysteine – one of the strongest predictors of dementia and Alzheimer’s.

The Hidden Brain Risk – Homocysteine

The homocysteine-raising effect is quite considerable. A group of doctors from University Hospital Nijmegen tested the effects of coffee by assigning volunteers to drink a litre of unfiltered coffee a day – that’s about four cups – for two weeks. At the start of the two weeks, their average homocysteine score was 12.8 µM, slightly above the national average of 10 to 11. At the end of the two weeks, their homocysteine score was 14. (1)

This homocysteine-raising effect was confirmed in another study by Dr Verhoef and colleagues at the Wageningen Centre for Food Sciences in the Netherlands, which showed that two cups of coffee increased homocysteine by 11% after four hours. Interestingly, caffeine tablets without coffee increased it by only 5%, suggesting that other compounds in coffee, such as theophylline and theobromine (also found in chocolate), may play a role. (2)

This means that if your homocysteine is already slightly raised, perhaps above 9 or 10, drinking coffee may be doing more harm than good, since the brain starts shrinking with homocysteine levels above 11. Also, if you do drink a lot of coffee, it’s a good reason to check your homocysteine level. 
(Order your homocysteine test here. An accurate and simple way to check your level via a quick pinprick test.)

How Much Coffee is Too Much?

So, does coffee protect against dementia – or put you at greater risk? The answer depends on quantity.  A UK Biobank study involving 400,000 participants compared those drinking 1-2 cups a day with those drinking six or more cups a day and found both a 53% increased risk of dementia and smaller brain volumes in those drinking 6 or more cups.(3)  The UK Biobank didn’t measure the homocysteine of the participants, but this is the most plausible mechanism.

A new 2025 analysis from the US NHANES database reached a similar conclusion: higher coffee consumption was associated with a greater risk of dementia (4).

Yet the story isn’t entirely one-sided. A review of all studies up to 2020 concluded: “Caffeine effects were more often positive when consumed in moderate quantities (100–400 mg/day), consumed in the form of coffee or green tea, and in women.” (5)  The most recent UK Biobank findings confirmed that moderate coffee or tea drinkers had a lower risk of cognitive decline than abstainers. (6)

A double espresso delivers 200–300 mg of caffeine, so moderation seems to mean no more than two to two and a half cups a day — and only if unsweetened.

Sweetened or Unsweetened – Does it Matter?

It matters a lot. The UK Biobank found a modest reduction in risk in those drinking up to 2.5 cups a day, compared with non-coffee consumers, but only in those drinking unsweetened coffee. Those drinking sweetened coffee had a higher risk. (7)

This is consistent with research at Canada’s University of Guelph. Participants were given a carbohydrate snack – such as a croissant, muffin, or toast – together with either a decaf or regular coffee. Those having the coffee-carb combo had triple the increase in blood sugar levels. In addition, insulin sensitivity, the hormone that controls blood sugar levels, was almost halved. (8)  The lesson? Enjoy your coffee on its own, without sugar or a carb-laden pastry.

Don’t Drink Coffee on Waking

Timing also matters. In the first hour after waking, your body naturally peaks in cortisol, the long-acting adrenal hormone that gets you going. (9)  That is why it is probably better not to have coffee, which further promotes adrenal hormones, for at least an hour after waking. Otherwise, you may stop producing enough of your own cortisol and become dependent on the caffeine hit.

In the evening, it’s the opposite story. Cortisol should be reducing and melatonin rising, but caffeine can affect this for up to 10 hours. The results? Over time, poorer sleep, which can contribute to a whole host of health problems, and greater difficulty waking in the morning, leading to a cycle of dependency on coffee.

One cup of coffee a day, in the morning, ideally not on waking but at least 30 to 60 minutes later, seems optimal. (10) However, the more tea you drink, the better, according to two studies, with green tea being the most beneficial.(11, 12)  This benefit, however, was not found in a UK Biobank study, which reported tea and coffee drinking to be associated with worsening cognition compared with abstainers.(13) 

The Japanese have a tradition of making a pot of green tea and, if they want a second, simply add hot water to the teapot. I do the same with coffee – if I have a second cup I run the coffee through the filter paper again. In this way it is progressively weaker.

But let’s be honest: coffee is an addictive stimulant and, while it may not be as harmful as alcohol, it is ultimately an energy robber. Having used coffee to help me through an intense month of early mornings and book writing, I quit and experienced a severe withdrawal headache that lasted 36 hours!

My Advice for the ‘Wired and Tired”

or those stuck in the vicious cycle – wired by coffee to stay awake, then relying on alcohol to switch off at night – my advice is simple: reset. Quit both for a time. Focus on consuming a low-sugar, low GL diet, along with supplements including B vitamins, plus extra vitamin C and omega-3 fish oil. All this advice and more is provided when you become a FRIEND of Food for the Brain and gain access to your six-month COGNITION™ brain upgrade programme. Click here to find out more.

Andrew was a case in point. Managing a chain of supermarkets had left him very stressed.

During the day, he drank coffee and in the evening, he relaxed with a beer or some wine as otherwise he would struggle to sleep. He was also gaining weight.

Andrew went on a low-GL diet, quit drinking coffee and alcohol, and took the recommended supplements. Three weeks later, he said: “My energy is through the roof, I don’t feel stressed, have no problem sleeping and I’m waking refreshed.” 

In Short …

One to two cups of unsweetened coffee a day, taken 30–60 minutes after waking, is probably optimal.
Avoid combining coffee with sugar or high-carbohydrate foods.  
Test your homocysteine levels, especially if you drink more than two cups a day.
Buy a single homocysteine test here or get it along with other important brain biomarkers in the DRIfT 5-in-1 test kit here (for best value).
Consider switching to green tea or more weakly brewed coffee where possible for a gentler stimulant effect.
Avoid caffeinated drinks after noon, especially if you have difficulty getting to sleep or staying asleep.
If you rely on caffeine to function or alcohol to unwind, it may be time for a reset.

Food for the Brain is a not-for-profit educational and research charity that offers a free Cognitive Function Test and assesses your Dementia Risk Index to be able to advise you on how to dementia-proof your diet and lifestyle.

By completing the Cognitive Function Test you are joining our grassroots research initiative to find out what really works for preventing cognitive decline. We share our ongoing research results with you to help you make brain-friendly choices.

Please support our research by becoming a Friend of Food for the Brain.

References:

(1) Grubben MJ, Boers GH, Blom HJ, Broekhuizen R, de Jong R, van Rijt L, de Ruijter E, Swinkels DW, Nagengast FM, Katan MB. Unfiltered coffee increases plasma homocysteine concentrations in healthy volunteers: a randomized trial. Am J Clin Nutr. 2000 Feb;71(2):480-4. doi: 10.1093/ajcn/71.2.480. PMID: 10648261. https://pubmed.ncbi.nlm.nih.gov/10648261/

(2) Verhoef P, Pasman WJ, Van Vliet T, Urgert R, Katan MB. Contribution of caffeine to the homocysteine-raising effect of coffee: a randomized controlled trial in humans. Am J Clin Nutr. 2002 Dec;76(6):1244-8. doi: 10.1093/ajcn/76.6.1244. PMID: 12450889. https://pubmed.ncbi.nlm.nih.gov/12450889/

(3) Pham K, Mulugeta A, Zhou A, O’Brien JT, Llewellyn DJ, Hyppönen E. High coffee consumption, brain volume and risk of dementia and stroke. Nutr Neurosci. 2022 Oct;25(10):2111-2122. doi: 10.1080/1028415X.2021.1945858. Epub 2021 Jun 24. PMID: 34165394. https://pubmed.ncbi.nlm.nih.gov/34165394/

(4) Li, J., Yu, K., Bu, F. et al. Exploring the impact of coffee consumption and caffeine intake on cognitive performance in older adults: a comprehensive analysis using NHANES data and gene correlation analysis. Nutr J 24, 102 (2025). https://doi.org/10.1186/s12937-025-01173-x

(5) Alida Chen J et al, Associations Between Caffeine Consumption, Cognitive Decline, and Dementia: A Systematic Review Journal of Alzheimer’s Disease 78 (2020) 1519–1546 DOI 10.3233/JAD-201069 https://pubmed.ncbi.nlm.nih.gov/33185612/

(6)Rainey-Smith SR, Sewell KR, Brown BM, Sohrabi HR, Martins RN, Gardener SL. Moderate coffee and tea consumption is associated with slower cognitive decline. J Alzheimers Dis. 2025 Jul 21:13872877251361058. doi: 10.1177/13872877251361058. Epub ahead of print. PMID: 40686251.

(7) Tingjing Zhang, Jiangen Song, Zhenfei Shen, Kewan Yin, Feifei Yang, Honghao Yang, Zheng Ma, Liangkai Chen, Yanhui Lu, Yang Xia,

Associations between different coffee types, neurodegenerative diseases, and related mortality: findings from a large prospective cohort study, The American Journal of Clinical Nutrition, Volume 120, Issue 4, 2024, Pages 918-926, ISSN 0002-9165, https://doi.org/10.1016/j.ajcnut.2024.08.012. https://ajcn.nutrition.org/article/S0002-9165(24)00671-3/abstract

(8) Moisey LL, Kacker S, Bickerton AC, Robinson LE, Graham TE. Caffeinated coffee consumption impairs blood glucose homeostasis in response to high and low glycemic index meals in healthy men. Am J Clin Nutr. 2008 May;87(5):1254-61. doi: 10.1093/ajcn/87.5.1254. PMID: 18469247. https://pubmed.ncbi.nlm.nih.gov/18469247/

  (9) Debono M, Ghobadi C, Rostami-Hodjegan A, Huatan H, Campbell MJ, Newell-Price J, Darzy K, Merke DP, Arlt W, Ross RJ. Modified-release hydrocortisone to provide circadian cortisol profiles. J Clin Endocrinol Metab. 2009 May;94(5):1548-54. doi: 10.1210/jc.2008-2380. Epub 2009 Feb 17. PMID: 19223520; PMCID: PMC2684472. https://pubmed.ncbi.nlm.nih.gov/19223520/   

(10) Xuan Wang, Hao Ma, Qi Sun, Jun Li, Yoriko Heianza, Rob M Van Dam, Frank B Hu, Eric Rimm, JoAnn E Manson, Lu Qi, Coffee drinking timing and mortality in US adults, European Heart Journal, 2025;, ehae871, https://doi.org/10.1093/eurheartj/ehae871 

(11)  Nurk E, Refsum H, Drevon CA, Tell GS, Nygaard HA, Engedal K, Smith AD. Intake of flavonoid-rich wine, tea, and chocolate by elderly men and women is associated with better cognitive test performance. J Nutr. 2009 Jan;139(1):120-7. doi: 10.3945/jn.108.095182. Epub 2008 Dec 3. PMID: 19056649 https://pubmed.ncbi.nlm.nih.gov/19056649/ 

(12) Feng L, Chong MS, Lim WS, Lee TS, Kua EH, Ng TP. Tea for Alzheimer Prevention. J Prev Alzheimers Dis. 2015;2(2):136-141. doi: 10.14283/jpad.2015.57. PMID: 29231231. https://pubmed.ncbi.nlm.nih.gov/29231231/ 

(13) Cornelis MC, Weintraub S, Morris MC. Caffeinated Coffee and Tea Consumption, Genetic Variation and Cognitive Function in the UK Biobank. J Nutr. 2020 Aug 1;150(8):2164-2174. doi: 10.1093/jn/nxaa147. PMID: 32495843; PMCID: PMC7398783.  https://pmc.ncbi.nlm.nih.gov/articles/PMC7398783/