Don't treat giving blood as a health measure: there is no randomized trial behind “detox, lower blood fats, prevent heart attack,” and giving too often really does leave you short of iron

Cost

Free. One donation, with the form, the draw and a rest for observation afterward, takes about an hour. For several weeks afterward, the body keeps replacing the iron it lost.

What you get

The Kuopio study in Finland followed 2862 men aged 42 to 60 for nearly 9 years on average. Of the 153 who had donated blood in the 24 months before counting began, 1 person (0.7%) had an acute heart attack. Of the 2529 who had not, 316 (12.5%) did (difference between the two shares P<0.0001). After removing the effects of age and other coronary risk factors, the heart attack risk of those who had donated was about 88% lower. Relative risk 0.12 (95% CI 0.02–0.86, P=0.035). But this came from tracking records, with no comparison group. The Nordic SCANDAT database had 1,182,495 blood donors, followed for a total of 9,526,627 person-years, during which 15,401 died. When only traits such as age and sex were removed, each extra donation a year was linked to an 18.6% lower death rate (95% CI 16.8%–20.4%). When the further layer of “you are only allowed to keep donating if you stay healthy” was also removed, the drop shrank to 7.5% (5.7%–9.4%). The authors' conclusion was that it “cannot be interpreted as firm evidence of a health benefit.” The FeAST randomized controlled trial enrolled 1277 people with symptomatic lower-limb artery disease and randomly split them into two groups, one with regular bloodletting every 6 months to reduce iron and one as a comparison. The main outcome was death from all causes, 125/636 (20%) versus 148/641 (23%). HR 0.85 (HR is the hazard ratio; 1 means the two sides are the same). 95% CI 0.67–1.08, P=0.17. Death plus nonfatal heart attack and stroke combined was 180 (28%) versus 205 (32%), HR 0.88 (0.72–1.07, P=0.20). Neither showed a difference. The INTERVAL randomized trial enrolled 45,263 whole-blood donors, split into three donation intervals. For men these were 12 weeks, 10 weeks and 8 weeks, and for women 16 weeks, 14 weeks and 12 weeks. With shorter intervals, noticeably more blood was collected over two years (men in the 8-week group gave 1.69 more units than the 12-week group, 95% CI 1.59–1.80). Quality of life, physical activity and cognitive function showed no difference across groups. But donors had more discomfort, including fatigue, shortness of breath, faintness, dizziness and restless legs (legs so uncomfortable at night you cannot lie still). Mean hemoglobin and ferritin were also lower, and more donations were deferred because of low hemoglobin (P<0.0001 for each). Iron deficiency affects how the body makes heat: 10 women with iron-deficiency anemia, 8 people whose iron stores were used up but who were not yet anemic, and 12 control women sat in 28 ℃ water for 100 minutes. The anemic group's rectal temperature was 36.0±0.2 ℃, versus 36.2±0.1 ℃ in controls (P=0.001). Oxygen consumption was 5.28±0.26 versus 5.99±0.29 mL·min⁻¹·kg⁻¹ (P=0.04). The two thyroid hormones, thyroxine and triiodothyronine, were also lower (P<0.002). The claim seems to hold up because blood donors are healthy people who have been screened again and again, and the hypothesis that “letting out iron protects the heart” did not pass in randomized trials

Notes

What is being ruled out is “giving blood for the sake of your own body,” not giving blood itself. Blood is for others to use, and by this book's tiers of who benefits, it falls in tier 4 (strangers). What can come back to you is the part the system provides. Article 14 of the Blood Donation Law (献血法) provides that voluntary donors who themselves use blood in a hospital are exempt from the collection, storage, separation and testing fees, and that spouses and direct relatives are exempt or pay less according to the provincial government's rules. A January 2024 notice from the National Health Commission (国家卫健委) states that 28 provinces have reached the point where the blood costs of voluntary donors and their relatives in hospitals within the province are reduced or waived directly at discharge. People who receive the Voluntary Blood Donation Contribution Award (无偿献血奉献奖) can also, under the local “three exemptions” (三免) policy, ride public transport free, enter government-funded parks free, and be exempt from the ordinary outpatient consultation fee at public hospitals. If you give, follow the legal interval. Article 9 of the Blood Donation Law provides that each donation is generally 200 milliliters and at most 400 milliliters. The interval between two donations must be no less than 6 months. The encouraged age is 18 to 55. Don't squeeze the interval to the minimum to chase an honor or a group quota. Women, people with low body weight and people with heavy periods already run tight on iron, and people who donate repeatedly can pay for a ferritin check. If you stay tired or sensitive to cold after donating, or at night lie down with a leg discomfort so strong you cannot help moving them (this is called restless legs), don't guess that your “vital energy is hurt”; get a blood count and a ferritin test. If iron deficiency is found, take iron as your doctor says and lengthen the interval between donations. The human evidence for the cold-sensitivity part comes from only 10 people, and is used to explain why it happens, not to say how many people it happens to

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

1. Salonen JT, Tuomainen TP, Salonen R, Lakka TA, Nyyssönen K (1998). Donation of blood is associated with reduced risk of myocardial infarction. The Kuopio Ischaemic Heart Disease Risk Factor Study. American Journal of Epidemiology, 148(5), 445-451. https://doi.org/10.1093/oxfordjournals.aje.a009669
2. Ullum H, Rostgaard K, Kamper-Jørgensen M, et al. (2015). Blood donation and blood donor mortality after adjustment for a healthy donor effect. Transfusion, 55(10), 2479-2485. https://doi.org/10.1111/trf.13205
3. Zacharski LR, Chow BK, Howes PS, et al. (2007). Reduction of iron stores and cardiovascular outcomes in patients with peripheral arterial disease: a randomized controlled trial. JAMA, 297(6), 603-610. https://doi.org/10.1001/jama.297.6.603
4. Di Angelantonio E, Thompson SG, Kaptoge S, et al. (2017). Efficiency and safety of varying the frequency of whole blood donation (INTERVAL): a randomised trial of 45 000 donors. Lancet, 390(10110), 2360-2371. https://doi.org/10.1016/S0140-6736(17)31928-1
5. Beard JL, Borel MJ, Derr J (1990). Impaired thermoregulation and thyroid function in iron-deficiency anemia. American Journal of Clinical Nutrition, 52(5), 813-819. https://doi.org/10.1093/ajcn/52.5.813
6. 全国人大常委会 (1997). 中华人民共和国献血法（第二、九、十四条）. https://flk.npc.gov.cn/detail?id=2c909fdd678bf17901678bf5e71801f9
7. 国家卫生健康委等 (2024-01-08). 关于进一步做好无偿献血者激励奖励工作的通知. https://www.gov.cn/zhengce/zhengceku/202401/content_6924875.htm

Translated from the Chinese original. Original book, section 6, tip 17. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer