The Merry Nervous System: The Research
The holidays,
measured.
What 18
studies show.
Eighteen peer-reviewed studies on giving, gifts, money, traditions, heart health and the family table, and what each one can and can’t tell you.
Every study is labeled by how it was run and carries a fine-print line on its limits. Each set of three ends in one simple practice. No lock, no email.
The evidence tree.
Eighteen studies, hung as ornaments. Each branch is one question. The color is how the study was run. The size is how many people were in it, so you can see at a glance which findings rest on nineteen people in a scanner and which on a national registry.
Under the tree: one prescription per branch.
The Christmas Eve spike.
Sweden logged 283,014 heart attacks over sixteen years, most timed to the minute. When researchers lined them up against the calendar, one night stood out.
New Year’s Eve. Easter. Major football tournaments and the Olympics.
People over 75, and people with diabetes or heart disease.
Midsummer (+12%), early mornings, and Mondays.
Chest pain, pressure, or a racing, uneven heartbeat means call 911 now. Not after dinner. Not after the holiday.
Mohammad et al. (2018), The BMJ, 363, k4811, doi.org/10.1136/bmj.k4811. The +37% is the paper’s own figure (incidence rate ratio 1.37, 95% CI 1.29 to 1.46). The daily averages are as reported in coverage of the paper; the other two percentages are worked out from them. This is observational: it shows when heart attacks cluster, not why. In Sweden the main celebration is Christmas Eve. In the United States, a study of 53 million death records found cardiac deaths peaking on Christmas Day, the day after, and New Year’s Day (Phillips et al., 2004, on this page). Education, not medical advice.
The evidence map.
Every study again, plotted by the question it asked and how it was run. The hatched squares are honest gaps. Pick a ring to read its finding, then open the full card with its fine print.
The honest number.
One study can flatter an idea. A meta-analysis pools every study it can find, and that is where the hype usually shrinks. Here is what two of them say about kindness and the person doing it. Pick a row to see what that size looks like.
Both pooled estimates sit near the small line. Giving will not fix a hard December. It nudges.
The nudge shows up across 27 experiments and 201 samples, and informal, spontaneous helping showed a stronger link than formal volunteering.
In 2020 the original $5 team reran their work at scale. 712 students who bought something for someone else felt happier than those who bought for themselves. 1,950 adults who only recalled a past purchase did not.
Curry et al. (2018), Journal of Experimental Social Psychology, 76, 320–329, doi.org/10.1016/j.jesp.2018.02.014 · Hui et al. (2020), Psychological Bulletin, 146(12), 1084–1116, doi.org/10.1037/bul0000298 · Aknin, Dunn, Proulx, Lok & Norton (2020), Journal of Personality and Social Psychology, 119(2), e15–e26, doi.org/10.1037/pspa0000191. The small, medium and large lines are Cohen’s conventional benchmarks (0.2, 0.5, 0.8). These reviews are context for the eighteen studies below; they are not counted among them.