High cholesterol remains extraordinarily common. Between 2017 and 2020, approximately 86.4 million U.S. adults had total cholesterol of at least 200 mg/dL, while 63.1 million had LDL cholesterol (LDL-C) of at least 130 mg/dL. Globally, high LDL-C was associated with an estimated 3.65 million cardiovascular deaths and 87.7 million disability-adjusted life years in 2021. The cardiovascular consequences develop over time because atherosclerotic risk rises with both the concentration of circulating LDL and the duration of exposure, allowing the effect of elevated LDL to accumulate across years and decades.
Even so, cholesterol itself is indispensable to the body. It is an essential structural component of cell membranes, and cholesterol metabolism supplies sterols used in processes including steroid-hormone and bile-acid synthesis. Cells therefore have to synthesize, absorb, store, export, and redistribute cholesterol while keeping its concentration within tightly regulated ranges. In circulating blood, cholesterol travels within lipoprotein particles, including low-density lipoprotein (LDL) and other particles that contain apolipoprotein B (ApoB).
LDL-C therefore captures only one part of atherogenic lipoprotein burden. LDL-C estimates the amount of cholesterol being carried within LDL particles, whereas ApoB more closely reflects the number of circulating atherogenic particles because each LDL, very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and lipoprotein(a) particle contains one ApoB molecule. Those measures often track together, but LDL particles do not all carry the same amount of cholesterol, so LDL-C can underestimate particle burden when relatively cholesterol-poor particles predominate, as can occur in metabolic syndrome, diabetes, and hypertriglyceridemia.
The arterial wall is where prolonged exposure becomes disease. LDL and other ApoB-containing particles can cross into the arterial intima, and atherosclerosis begins when some of those particles become retained rather than returning to the circulation. Retained lipoproteins can undergo oxidative, enzymatic, and other modifications that alter their interactions with vascular and immune cells, promoting endothelial activation, recruitment of monocytes, and uptake of lipid by macrophages. As macrophages continue taking up modified lipoproteins, cholesterol accumulates and the cells can develop into lipid-filled foam cells that become part of the growing atherosclerotic lesion. Greater numbers of circulating ApoB particles and longer exposure give this process more opportunity to occur, providing a biological explanation for the cumulative relationship between LDL burden and cardiovascular risk.
Macrophages also have mechanisms for moving cholesterol back out. The transporter ABCA1 can move cholesterol from cholesterol-loaded macrophages to lipid-poor apolipoprotein A-I and nascent high-density lipoprotein (HDL) particles, beginning a pathway through which excess cholesterol can ultimately be transported away from peripheral tissues. HDL also has experimentally measurable antioxidant, anti-inflammatory, endothelial-protective, and antiapoptotic activities that are not captured by the amount of cholesterol contained inside an HDL particle. In 2,924 adults followed for a median of 9.4 years in the Dallas Heart Study, cholesterol-efflux capacity was inversely associated with subsequent cardiovascular events even after adjustment for HDL-C and other cardiovascular risk factors, illustrating why HDL concentration and HDL function are not interchangeable measurements.
These processes create several points at which cholesterol biology can change before an artery becomes visibly obstructed: how many atherogenic particles circulate, what happens to those particles after they enter the arterial wall, how strongly modified LDL activates vascular and immune cells, how much cholesterol macrophages accumulate, and how effectively that cholesterol can be exported again.
Early molecular hydrogen (H₂) studies reported changes at several of these points rather than only shifting total cholesterol on a conventional lipid panel. The first controlled human evidence appeared in people already experiencing metabolic dysfunction. In a randomized, double-blind, placebo-controlled crossover trial, 30 people with type 2 diabetes and six with impaired glucose tolerance consumed 900 mL per day of hydrogen-rich water for eight weeks, separated by a 12-week washout period. Hydrogen-rich water reduced modified LDL by 15.5%, small dense LDL by 5.7%, and urinary 8-isoprostanes by 6.6%, while oxidized LDL showed a nonsignificant downward trend. The lipid signal in this study therefore involved characteristics of LDL associated with particle composition and oxidative modification, two features that influence how circulating lipoproteins interact with the metabolic and vascular environment.
Five years later, researchers examined what happened on both sides of cholesterol transport. Twenty people with potential metabolic syndrome consumed 0.9–1.0 L of hydrogen-rich water per day for 10 weeks, after which total cholesterol and LDL-C were lower and serum ApoB100 and ApoE had also decreased. HDL isolated from the participants after the intervention provided greater protection against LDL oxidation, reduced TNF-α-induced monocyte adhesion to endothelial cells, increased cholesterol efflux from macrophage foam cells, and better protected endothelial cells from TNF-α-induced apoptosis. Serum superoxide dismutase increased, while markers of lipid oxidation decreased in whole serum and LDL. However, this was an uncontrolled before-and-after study, so the changes cannot be attributed to H₂ with the same confidence as they could in a placebo-controlled trial.
A subsequent trial tested those findings under randomized, placebo-controlled conditions in people selected specifically for high cholesterol. Sixty-eight adults with untreated isolated hypercholesterolemia were randomized to hydrogen-rich water or placebo water for 10 weeks. HDL isolated from participants receiving H₂ showed greater ABCA1-dependent cholesterol efflux, and circulating pre-β-HDL increased even though HDL-C itself did not change significantly. The HDL samples also showed greater protection against LDL oxidation, oxidized-LDL-induced inflammation, and endothelial-cell apoptosis, while plasma ApoB100 decreased and ApoM increased. A greater proportion of participants receiving H₂ experienced reductions in total cholesterol and LDL-C than participants receiving placebo, with response rates of 47.1% versus 17.7% for total cholesterol and 47.1% versus 23.5% for LDL-C.
Later trials suggest that H₂ can also influence conventional lipid measurements, although the response has not been uniform. In adults with metabolic syndrome, 24 weeks of hydrogen-rich water reduced total cholesterol and triglycerides. An eight-week randomized trial in adults with obesity also reported reductions in total and LDL cholesterol compared with control water. However, a 2026 meta-analysis of 13 randomized trials involving 757 participants placed these results in perspective: hydrogen-rich water reduced total cholesterol by an average of 6.71 mg/dL and LDL-C by 3.21 mg/dL, with no significant reduction in triglycerides and a small decrease in HDL-C. The authors therefore considered the average lipid-lowering effect statistically significant but clinically modest.
The experimental literature is informative about why these human studies detected changes in lipoprotein function. In ApoE-knockout mice, H₂ reduced non-HDL cholesterol and ApoB, increased proteins involved in hepatic cholesterol and bile transport, improved HDL-mediated cholesterol efflux, and reduced arterial lipid deposition. A separate study that tracked radiolabeled cholesterol from macrophages through the circulation, liver, bile, and feces found that H₂ partially restored reverse cholesterol transport and HDL-mediated cholesterol efflux impaired by cigarette smoke. These findings provide a plausible experimental counterpart to the increased macrophage cholesterol efflux measured with HDL isolated from participants in some of the human trials, although they do not establish that the same mechanism occurred in those participants.
H₂ has also affected what happens after LDL becomes modified and enters the arterial environment. In endothelial cells exposed to oxidized LDL, H₂ suppressed LOX-1 and NF-κB signaling together with oxidative stress, inflammatory mediators, and adhesion molecules involved in immune-cell recruitment. In macrophages, H₂ restored oxidized-LDL-impaired autophagic flux and reduced inflammatory signaling through a pathway involving SIRT1. In LDL-receptor-knockout mice, H₂ additionally reduced oxidized LDL, foam-cell apoptosis, oxidative stress, and endoplasmic-reticulum stress while activating Nrf2, and plaques contained more collagen with less lipid and macrophage accumulation. Other atherosclerosis-prone mouse models have similarly shown reduced aortic lesion burden, oxidative stress, macrophage infiltration, and vascular-cell senescence after H₂ exposure.
The liver may provide another route through which H₂ influences circulating lipid metabolism. In people with non-alcoholic fatty liver disease, hydrogen–oxygen inhalation improved serum lipids, liver enzymes, and liver fat in participants with more advanced disease, while parallel animal and cell experiments showed that blocking autophagy weakened the effects of H₂ on hepatic injury and intracellular lipid accumulation. This does not establish autophagy as the explanation for the LDL-C or ApoB changes reported in other trials, but it links H₂ with hepatic lipid handling as well as events occurring within circulating lipoproteins and the arterial wall.
Taken together, the H₂ literature points to effects across several interconnected parts of cholesterol and lipoprotein biology. Human studies have reported changes in ApoB-containing particles, modified and small dense LDL, HDL-mediated cholesterol efflux, and other measures of HDL function, while experimental studies extend those findings into reverse cholesterol transport, oxidized-LDL signaling, macrophage cholesterol handling, and atherosclerotic plaque biology. The reductions in conventional measures such as LDL-C have generally been modest, but those measurements capture only one part of the response described across these studies. The emerging picture is therefore less about H₂ acting as a conventional cholesterol-lowering agent and more about its potential influence on how lipoproteins are modified, transported, cleared, and handled within the vascular environment. Whether these changes ultimately slow atherosclerotic progression or reduce cardiovascular events in humans has not yet been established.
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