A warning from UnitedHealth executives on Wednesday that demand for medical services was rising sent insurance stocks tumbling and, in turn, hit investors who bet on health care. Shares of UnitedHealth fell more than 6% on Wednesday after CFO John Franklin Rex warned at a conference that the company’s medical loss ratio for the second quarter could come in at the high end or above prior guidance due to heavy demand, especially for outpatient procedures. Humana and CVS Health were also hit, falling 11.2% and 7.8%, respectively. “This is straight-up care activity, not cost per case. So we’re not seeing anything on the acuity level, but certainly a meaningfully higher number of cases that are being performed is what we’re seeing,” Rex said, according to a recording provided by FactSet. Rising health spending would seem to be a good thing for investors who bet on the sector, but that’s not how Wednesday’s trading played out. The biggest health care ETF — the $41 billion Health Care Select Sector SPDR Fund (XLV) — lost 1% on Wednesday. The $17 billion Vanguard Health Care ETF (VHT) also fell about 1%. XLV 5D mountain The XLV was dragged down by insurance stocks on Wednesday. The issue is that the largest holding in the XLV is UnitedHealth Group, at about 9% of the fund. CVS, Cigna and Humana all account for more than 1% of the fund as well. The VHT also has UnitedHealth as its top holding. Some health care funds with a narrower scope had more success. For example, the iShares US Medical Devices ETF (IHI) rose 1% on Wednesday. That fund has Thermo Fisher Scientific and Abbott Laboratories as its top holdings. To be sure, Wednesday’s divergence between the XLV and the IHI could be short-lived. Rex said that the increased demand could be a lagged result of the hospital restrictions during the pandemic, which means the increased demand may soon abate. And some Wall Street analysts said the dramatic sell-off in typically stodgy insurance stocks could prove to be a buying opportunity. “We see this as a rare opportunity to get some of the highest-quality services companies at a discounted price; the comments on utilization do not change our long-term view,” Cantor Fitzgerald analyst Sarah James said in a note to clients. — CNBC’s Michael Bloom contributed to this report.