Dry eyes are caused by a lack of tear production or fast evaporation. One method for managing the systems is to use “artificial tear” products—eye drops that can lubricate eyes. Hyaluronic acid (HA) has been investigated as a component of artificial tear products due to its ability to bind to ocular surface cells, enhance wound healing, and reduce the viscosity of the overall fluid.
A 2021 meta-analysis of randomized, controlled trials on participants with dry eye syndrome compared eye drops containing HA with eye drops not containing HA, including many artificial tear products with other ingredients. Hyaluronic acid improved tear production relative to saline and some artificial tear products, but not all artificial tear products. The same was true of tear break-up time and Ocular Surface Disease Index, while an analysis comparing HA products to those without HA didn’t find a difference for Corneal Fluorescein Staining Score. Trials where HA is compared to artificial tear products are often confounded with other ingredients that make it difficult to discern the efficacy of HA. A 0.3% HA solution appeared to be the most effective relative to saline, though the evidence doesn't allow us to say that this dose is the best with much certainty. Doses as low as 0.1% have seen some benefit and may be useful as an addition to multi-ingredient artificial tear products, though much more research with the proper study design is needed to evaluate the ideal formulae.
Hyaluronic acid is likely a beneficial ingredient in eye drops intended to treat dry eye syndrome, and a high dose solution (0.3%) may be especially useful. In addition, artificial tear products that contain hyaluronic acid may be optimal, though much more evidence is needed to establish the ideal formulae.
A meta-analysis of 7 studies and 2664 participants found that higher hyaluronic acid levels were associated with worse cancer prognosis, including survival and progression. The direction of causality is unknown, however. This is also highly unlikely to reflect supplemental intake, as the vast majority of people don’t take hyaluronic acid supplements and instead may be the result of cancer cells stimulating themselves or nearby cells to synthesize hyaluronic acid.
A considerably higher level of HA has been seen in ovarian tumors compared with normal ovarian tissue, to an extent that could only be explained due to tumors accumulating more hyaluronic acid—123x more in grade 3 tumors than normal ovaries.
Beyond the total level, the effects of hyaluronic acid on cancer may depend on its molecular weight, a measure of how many hyaluronic acid molecules are chained together. In general, low molecular weight hyaluronic acid chains seem to play a larger role in cancer than high molecular weight hyaluronic acid chains.
A study on breast cancer patients, for example, found that higher amounts of low molecular weight hyaluronic acid, but not hyaluronic acid in general, were associated with cancer metastasis. Another interesting observation comes in the form of naked mole rats, who synthesize large amounts of hyaluronic acid in chain lengths around 5 times longer than those in humans and mice. Naked mole rats are known to be highly resistant to cancer, seemingly due in part to the unique nature of their hyaluronic acid. Still, conflicting results exist regarding the role of hyaluronic acid chain length and ultimately research on humans is limited.
One study has found that hyaluronic acid can play a part in pancreatic cancer cell growth in the context of glutamine-fructose 6-phosphate amidotransferase 1 (GFAT1) knockout pancreatic ductal adenocarcinomas cell lines. Suppressing GFAT1 may be a method to suppress the metabolism and growth of these cancer cells. In the study, GFAT1 knockout was effective at starving the cells, but the addition of hyaluronic acid provided an alternative source of energy to the cells and fueled cancer cell growth. It is unclear whether or not this effect is relevant to cancer patients who are not on GFAT1 suppressing treatments or would be relevant in living humans at all.
Finally, it’s worth noting that there is almost no data on how ingesting hyaluronic acid impacts cancer. One study on mice with cancer reported that oral supplementation of hyaluronic acid, testing both low- and high-molecular-weight forms, had no effect on cancer growth or metastasis over the course of 28 days.
Hyaluronic acid levels increase in the context of cancer and may play some role in the growth of cancer cells. Low molecular weight hyaluronic acid in particular may be related to cancer growth. Despite this, It is unclear if supplementation makes a difference in the risk of getting cancer or the rate of growth.