As U.S. and South Korean intelligence teams investigate the sincerity of Kim Jong Un's newfound willingness to engage in a denuclearization dialogue, they are also tracking reports the North Korean dictator is dealing with a variety of health issues.

While there is little hard medical evidence, according to sources, Kim's family history, physical appearance and behavior in recent years have led to speculation he may suffer from a range of conditions including gout, diabetes, high blood pressure, a sexually transmitted disease and psychological issues.

“Kim’s health is something our own intel community is trying to gain every possible insight on,” said Harry Kazianis, director of defense studies at the Center for the National Interest. “There are rumors that Kim might have had plastic surgery and purposely gained weight to look more like his grandfather, the founding ruler of North Korea, and channel some his popularity.”

FILE - In this April 15, 2017, file photo, North Korean leader Kim Jong Un waves during a military parade in Pyongyang, North Korea. South Korea's military said Friday, Sept. 15, 2017 North Korea fired an unidentified missile from its capital Pyongyang that flew over Japan before landing in the northern Pacific Ocean. (AP Photo/Wong Maye-E, File) (Copyright 2017 The Associated Press. All rights reserved.)

U.S. intelligence sources acknowledged that piecing together an accurate “health profile” of Kim, who is around 35 years old, was not only “critical intelligence,” but also the “bread and butter” of scores of experts.

“Health conditions, including use of medicines or drugs, can impact a foreign leader’s decision-making and an expected death or debilitation of a leader can cause instability in a country with potential consequences for U.S. interests,” Bruce Klingner, senior research fellow for Northeast Asia at the Heritage Foundation's Asian Studies Center and former CIA deputy division chief for Korea, told Fox News.

So what is known about Kim's health?

North Korean officials in 2014 acknowledged he was suffering from an “uncomfortable physical condition” after footage was captured of him looking evidently heavier and walking with a pronounced limp. Experts quickly pointed to gout, which sparked speculation he also suffered from diabetes and high blood pressure.

“Kim Jong Un has gained a lot of weight, and this weight gain is believed to have brought many side effects, including heart disease and high blood pressure,” observed Eric Yoon, CEO and founder of Television Korea 24. “Kim often enjoys heavy drinking and smoking. In October 2014, he disappeared from the public and media for two months due to arthritic pain in his leg. But his health is top secret due to possible uprising in North Korea. Instead, he often just won’t appear in public.”

There are also unconfirmed reports Kim has a sexually transmitted disease. U.S intelligence sources told Fox News Kim's father was believed to have had a range of STDs, including syphilis, and that it is ”possible” the son may have the same.

North Korean leader Kim Jong Un speaks during a ceremony to award party and state commendations to nuclear scientists, technicians, soldier-builders, workers and officials for their contribution to what North Korea said was a succesful hydrogen bomb test, at the meeting hall of the Central Committee of the Workers' Party of Korea (WPK) in this undated photo released by North Korea's Korean Central News Agency (KCNA) on January 13, 2016. REUTERS/KCNA ATTENTION EDITORS - THIS PICTURE WAS PROVIDED BY A THIRD PARTY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THE AUTHENTICITY, CONTENT, LOCATION OR DATE OF THIS IMAGE. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS PICTURE IS DISTRIBUTED EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS. NO THIRD PARTY SALES. SOUTH KOREA OUT. NO COMMERCIAL OR EDITORIAL SALES IN SOUTH KOREA - RTX22B0G (REUTERS)

Speculation swirled around Kim Jong Il during his reign, as STDs reportedly rose to almost epidemic levels during the 1990s, when a calamitous famine sparked the growth of a sex industry desperate to make money.

The trend has reportedly continued within wealthier circles around Pyongyang, the North Korean capital. There are continued claims from South Korean news agencies that young girls are forced into prostitution to “service high-ranking North Korean officials,” making sex diseases all the more rampant among the military elite.

Then there is the issue of Kim's mental health, and what some see as signs of stress and even paranoia. Korean media regularly report on Kim's “insomnia,” and obsession with potential threats from people who many usurp his power.

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Kim Dong Yon, a former Republic of Korea Air Force officer and North Korean analyst, claimed a former chief doctor of Kim's grandfather, Kim il-Sung, asserted the former leader mandated frequent blood transfusions from young men with the same blood type “in order to support and improve the blood circulation.”

“Based on this, Kim Jong Un may go through similar medical treatments in order to improve his physical condition,” Yon speculated.

According to Yoon, Kim has a private doctor who resides in Bong Hwa Clinic and Hospital, located in Pyongyang. Bong Hwa is known to treat “only the top officials,” and the first family of North Korea.

“Kim has a team of doctors who cares for him and sometimes if need be, they will bring in foreign specialists from Russia, China, Singapore and Germany,” he said.

One U.S source said “what is fairly certain is that as far as access to health care and diet goes, he probably has access to the best that money can buy.”

Tom Fowdy, a marketing associate with China Global Connections and a North Korea analyst, concurred that while questions about the leader’s well-being are shrouded in guesswork, his family lineage offers plenty of red flags.

Late dictator, Kim Jong il

“His father Kim Jong il had serious problems in his final years, including diabetes, rumors of a stroke, cerebral hemorrhage, and of course died of a heart attack,” Fowdy said. “Grandfather Kim il-Sung’s health was best characterized by the presence of a growing calcium deposit on the back of his neck which grew to the size of a baseball. Due to the close proximity to his spine, it could not be operated on.”

Fowdy noted that North Korean photographers famously went to great lengths to try and hide the growth, with every picture of him taken from the left angle to conceal it.

“There are several sneaky photos where people caught it,” Foudy said. “However, if you wish to visit Kim il-Sung’s preserved body in the Kumsusan Palace of the Sun, the official state Mausoleum, you can see enough of his head to note the tumor is absent.”

When it comes to rogue regimes like North Korea, having proper intelligence reports and plans in place should Kim's health severely fail are crucial, sources said.

“We now develop a variety of scenarios – and some unlikely ones – as far as how he could fall from power and most importantly, who would likely replace him and in what manner,” said James Williamson, a retired Army special operations colonel and founder of OPSEC, a nonpartisan advocacy organization focused on protecting national intelligence assets.

One former high-ranking Pentagon official stressed contingency plans in the event of a Kim Jong un death are especially vital for a nuclear-armed adversary -- “finding out who would be in-charge or whether a civil war would ensue, finding out who is on what side, and working closely with China and South Korea to seize control of any nuclear sites.”

But when it comes to developing an accurate health assessment of the unpredictable leader, distinguishing fact from fiction is no easy feat.

“Within the intelligence community, North Korea is acknowledged to be the hardest of hard targets,” Klingner added. “Information, including the heath of Kim Jong Un, is difficult to come by and each intelligence source face considerable constraints in obtaining data on North Korea.”