What you do during the day determines how you sleep at night
Parts 1 and 2 covered the foundation: circadian rhythm, behavioral techniques, and the physical sleep environment. This post is about the daily inputs that shape sleep quality hours before you get anywhere near a bed.
Exercise, food, caffeine, alcohol. Everybody has opinions on them. But most of the conventional wisdom is either oversimplified or flat-out wrong. Let's take a look at the research for a more interesting (and more useful) story.
Exercise and Sleep
The "No Exercise Before Bed" Rule
For decades, the standard advice has been: don't exercise less than 3 hours before bedtime. Actual research on pre-sleep exercise timing is less clear.
One 2019 systematic review and meta-analysis of 23 studies concluded that evening exercise doesn't negatively affect sleep, instead significantly increasing slow-wave sleep (the deep, restorative stage).
Similarly, a 2021 meta-analysis specifically focused on evening high-intensity exercise confirmed that sessions completed 2 hours before bed may actually benefit sleep.
Conversely, a single very large study in 2025 (14,689 individuals across over 4 million person-nights) suggested that light exercise closer to bedtime has almost no impact, but high-intensity exercise within even 4 hours of sleep consistently disrupts autonomic recovery.
In other words, ¯\_(ツ)_/¯ .
When it comes to putting research to use in the real world, it's worth considering the size of the effects found, and how they fit into the bigger picture of fitness and health. Put simply, the benefits of just doing exercise at all far outweigh the impact of when you do it. If you want to play it safe, and it works for your schedule, you might still consider pushing at least your hard workouts to earlier in the day. If you can't, don't stress; the overall upside of exercise (for your life as well as your sleep) means you can just focus on getting in your workouts whenever you reliably can.
Dose-Response: More Isn't Always Better
The same meta-analyses found a U-shaped relationship between exercise dose and sleep quality. The sweet spot: roughly 150 minutes of moderate exercise per week (about 920 MET-minutes/week).
Long sessions (pushing past 60 minutes) often elevate cortisol and can create enough muscular fatigue to impair sleep quality, so more isn't always better.
And critically, the major benefits of exercise for sleep require 4–12 weeks of consistent training to materialize. You can't judge whether exercise is "helping your sleep" after one session.
For our clients, this usually means protecting a moderate, consistent exercise habit rather than chasing intense, sporadic workouts. Which, conveniently, is also what the longevity research says.
Caffeine
Your Genetics Determine More Than Your Habits
Caffeine has a population-average half-life of 5–6 hours. But that average obscures enormous individual variation: actual half-life ranges from 1.5 to 9.5 hours, driven by genes like CYP1A2.
If you carry the AA genotype of CYP1A2 (about 43% of people), you're a fast metabolizer. Caffeine clears your system roughly 4 times faster than it does for slow metabolizers. If you carry AC or CC (the other 57%), you're a slow metabolizer, and caffeine lingers much longer than you'd expect.
This and other similar genes are why some people can drink espresso after dinner and still pass out, while others are staring at the ceiling over their bed from a 2 PM coffee. It's not willpower or tolerance. It's genetics.
And it's why we do full genetic sequencing of all of our clients. Learn more about yourself once, and you can easily make choices that work for you for the rest of your life.
But the Research on Caffeine and Sleep Is Still Unambiguous
The landmark study here is Drake et al. (2013): 400 mg of caffeine (roughly a large Starbucks) consumed 6 hours before bedtime still reduced total sleep time by over an hour on objective measurement. And here's the critical finding: participants significantly underestimated the effect. They thought they slept fine. The polysomnography showed otherwise.
A 2023 systematic review and meta-analysis of 24 RCTs confirmed the pattern across studies: caffeine too close to bed reduces total sleep time by about 45 minutes, sleep efficiency by 7%, and deep sleep by about 11 minutes. It increases both the time it takes to fall asleep and the time spent awake during the night.
What is 'too close to bed?' Based on the full body of research, a good general recommendation is to cut out caffeine 8–9 hours before bedtime. (E.g., if you're a 10:30 PM sleeper, that means no caffeine after about 1:30 PM.) If you know you're a slow metabolizer (based on CYP1A2 allele or otherwise), you'd likely benefit from pushing the cutoff even earlier. But even if you're a fast metabolizer, you still have more left in your system than ideal if you push that cutoff beyond mid-afternoon.
One more thing we mentioned in the first post, but is worth repeating: caffeine doesn't actually give you energy, it just blocks adenosine receptors, masking the sleep pressure signal. With or without caffeine, your adenosine level keeps accumulating across the day. That's why, when the caffeine wears off, you hit an afternoon (or early evening) "crash": it's that masked sleep pressure hitting all at once.
Alcohol
The Most Socially Acceptable Sleep Saboteur
A few years back, this one was totally under the radar. Then enough people started wearing Whoop bands, Oura rings, and Apple Watches to spot the correlation themselves. By now, after endless articles and podcasts on the impact of alcohol on sleep, this 'insight' feels nearly trite.
Nonetheless, it's still a big lever, so we're recapping here. Alcohol feels like it helps sleep. After a couple of drinks, you'll often start feeling drowsy, because it enhances GABA-A receptor activity, producing genuine sedation. But as your body metabolizes the alcohol (at roughly one standard drink per hour), the sedative effect wears off and a sympathetic rebound kicks in. Cortisol rises. Heart rate elevates. Core temperature dysregulates. Acetaldehyde (a toxic byproduct of alcohol metabolism) accumulates.
The result: fragmented, shallow sleep in the second half of the night, exactly when you'd normally be getting most of your REM cycles. (A meta-analysis of 20 studies found delayed REM onset and reduced total REM sleep as the most consistent effect across all alcohol doses, starting even with just one or two standard drinks).
That REM impact is what matters most for this audience. REM is when your brain processes emotions, consolidates creative and associative memory, and recalibrates the amygdala. It's the stage responsible for the difference between waking up clear-headed versus waking up emotionally reactive and cognitively foggy. For executives and founders making high-stakes decisions, selectively eliminating REM is about the worst trade you can make.
(As we'll cover in the next post, and as your partner may already have pointed out to you, alcohol also sedates upper airway muscles, worsening snoring and sleep apnea.)
All that said, we're not teetotalers. Some great wine with dinner or a cocktail with friends can be among life's greatest pleasures. Just be aware of the impact of those drinks on your sleep (and your health overall), consider the trade-offs, and make sure you're getting real ROI on any single drink.
Some rough guidelines if you do decide to drink: try to leave 3–4 hours between your last drink and bedtime, limit to 1–2 standard drinks, and if you're tracking your sleep with a wearable, run the experiment yourself. Compare your HRV, resting heart rate, and sleep stages on drinking versus non-drinking nights; the data usually speaks for itself.
Nutrition and Meal Timing
Meal Timing (Revisited)
We covered this in Post 1 from a circadian perspective: late eating shifts peripheral clocks and suppresses melatonin by 30–50%. The practical rule (finish eating 3+ hours before bed) stands.
But there's an additional angle worth mentioning here. Eating close to bedtime, particularly high-carb or large meals, raises core body temperature through the thermic effect of food. As we covered in Post 2, your body needs to cool down to initiate sleep. A big meal works against that process at exactly the wrong time.
This doesn't mean you should go to bed hungry, which can also disrupt sleep. Just gun for smaller, protein-rich snacks closer to bedtime, and try to avoid large, late dinners.
Foods and Micronutrients With Specific Sleep Evidence
First, two foods with enough research to at least be worth keeping on your radar:
Tart cherry juice is the most-studied option. It contains natural melatonin (up to 13 ng/g), tryptophan, and anti-inflammatory anthocyanins. One polysomnography study found it increased sleep duration by as much as 84 minutes. A separate study showed 34 additional minutes of sleep with a measurable increase in circulating melatonin. The protocol in most studies: 8 oz of tart cherry juice concentrate twice daily (morning and evening). It's not a miracle, but the mechanism is plausible and the evidence is consistent.
Fatty fish and omega-3s also seems beneficial. A well-designed Oxford trial found that 600 mg of DHA daily for 16 weeks resulted in significantly improved sleep outcomes, with nearly an hour more sleep and fewer waking episodes. The mechanism likely involves omega-3's role in serotonin synthesis and neuronal membrane function. Eating fatty fish 2–3 times per week (or supplementing with a quality fish oil) has enough overlapping health benefits that the sleep data is a bonus rather than the sole justification.
Similarly, three micronutrients we routinely screen for:
Magnesium acts as a natural NMDA receptor antagonist and GABA agonist (in plain English: it calms neural activity). A meta-analysis of RCTs in older adults found magnesium supplementation reduced sleep onset latency by about 17 minutes versus placebo. The prevalence of subclinical magnesium deficiency is estimated at 50–80% in Western diets, making this one of the more likely deficiencies to find. We'll cover specific forms and dosing in the supplements post.
Iron (ferritin) is critical for anyone experiencing restless legs at night. Brain iron deficiency impairs dopamine synthesis, driving restless legs syndrome (which affects roughly 7% of the general population, probably higher among people who exercise intensely). If your serum ferritin is below 75 μg/L (also a surprisingly common finding), supplementation is warranted per international guidelines.
Finally, vitamin D deficiency is associated with worse sleep quality in meta-analyses, though the evidence for this one is a bit more mixed. Still, given the very high prevalence of deficiency, and all of the other ways vitamin D is important for health, worth getting this checked and addressed, too.
Things to Try Today
If you've been skipping evening workouts to "protect your sleep": Stop. Train when you can. If you want to play it safe, aim to finish high-intensity sessions at least 4 hours before bed. But the benefits of consistent exercise dramatically outweigh any acute timing effects, so don't make yourself nuts about it.
If you drink coffee after 2 PM: Push your cutoff earlier by an hour and hold it for two weeks. Track your sleep. Most people are surprised by the difference. If you want to get precise, test your CYP1A2 status, and factor that in to your cutoff timing.
If you have a nightcap habit: Run a two-week experiment: alternate drinking and non-drinking nights, and compare your wearable data the next morning. Most people don't need a meta-analysis once they see their own HRV numbers. Again, you don't necessarily need to give it up completely. Just be aware of the benefits and costs.
If you want a simple dietary addition: 8 oz of tart cherry juice concentrate in the morning and evening. Low-risk, plausible mechanisms, and the evidence (while not bulletproof) is directionally positive.
If you suspect a deficiency: Get ferritin, magnesium RBC, and vitamin D tested. These are common enough deficiencies that they're worth ruling out before adding other supplements.
If you eat dinner late: You already know the rule from Post 1: 3 hours before bed. If that's not realistic on weeknights, at least keep late meals small and protein-focused rather than large and carb-heavy.
What's Next
Exercise, nutrition, and timing are the behavioral inputs that set the stage for everything else. Get these right and you're removing the most common obstacles to good sleep before they ever reach the bedroom.
Next up: Supplements and Pharmacological Tools. Melatonin dosing (most people take 10–30x more than they need). The popular stacks, honestly evaluated. And the new class of prescription sleep medications that actually preserve sleep architecture instead of destroying it.
As always: the tools in this post work for most people, but "most people" isn't the same as you, specifically. That's why we built A3. From biomarker data to genetic insights, we use AI analysis and expert coaching to help clients figure out exactly which interventions will move the needle most for their particular physiology and then integrate them into their lives. If you want help building a personalized sleep protocol rather than experimenting on your own, we're here to help.