With the full implementation of the individual portion of the Patient Protection and Affordable Care Act less than five months away, physicians and doctor's offices around the country should be bracing for what could be an influx of new patients. With the mandate for insurance comes the potential that more people (both those covered under Medicaid expansion and self-insured individuals) may choose to visit their doctor more often to address ongoing and preventative concerns.

From an investing standpoint and as a society, we understand what diseases are most prevalent, where the trends are rising, and what medications are being developed to treat these diseases. Obesity, for instance, is a disease that affects 35.7% of the U.S. population, and with it comes a considerably higher risk of developing high blood pressure, high cholesterol, diabetes, and cancer. Similarly, some 25 million people in the U.S. are diabetic, with another nearly 80 million in a pre-diabetes stage. You'd think with staggering figures like these that the majority of doctors office visits would be related in some way to chronic weight or diabetic issues.

But that's just not the case, according to a large study conducted by the Mayo Clinic, which looked at 142,377 patients between 2005 and 2009 to determine why exactly they went to see their doctor. Your initial impression might be to assume that high-profile and prevalent diseases tend to be the main reason people go see their doctor, but it actually tends to be more subtle symptoms that drive us to seek help.

Here are the 10 most common reasons the Mayo Clinic listed in its study for why people go see their doctor :

1. Skin disorders, including cysts, acne, and dermatitis.

2. Joint disorders, including osteoarthritis.

3. Back problems.

4. Cholesterol problems.

5. Upper respiratory conditions (excluding asthma).

6. Anxiety, bipolar disorder, and depression.

7. Chronic neurologic disorders.

8. High blood pressures.

9. Headaches and migraines.

10. Diabetes.

Skin disorders

According to the Mayo Clinics' study, nearly 43% of respondents went to see their doctor in at least some context because of a dermatologic disorder. What this means for you as an investor is that there could be a huge growth potential in skin-disorder companies should more people choose to visit their physicians next year.

There are quite a few ways of profiting off skin disorders, since it's such a broad encompassing disorder that can range from aesthetic issues like acne to serious complications like melanoma. Beyond your commonly found over-the-counter medications, one interesting example of a potential beneficiary is Trius Therapeutics (NASDAQ: TSRX), the developer of experimental acute bacterial skin and skin structure infection drug, tedizolid. In trials, the drug, which is designed to treat methicillin-resistant staphylococcus aureus, better known as MRSA, reduced lesion sizes by at least 20% in 85.2% of patients in a 48-hour to 72-hour time period, which was slightly higher than Pfizer's (NYSE:PFE) Zyvox, which is the current standard of treatment. However, tedizolid achieved its results in just a six-day dosing period compared with Zyvox's 10-day standard treatment. With Cubist Pharmaceuticals agreeing to purchase Trius less than two weeks ago, it could be snagging itself quite the bargain.

On a larger scale, GlaxoSmithKline (NYSE:GSK) is also a big skin-disorder player, but primarily from the point of cancer treatment. Earlier this year, Glaxo received Food and Drug Administration approval for both Taflinar and Mekinist for the treatment of advanced melanoma. Both drugs are single agents (meaning either one or the other will be prescribed), with each targeting a BRAF mutation commonly found among melanoma patients. Not to mention that Glaxo also received FDA approval for its diagnostic test to determine whether patients possess this mutation. With few melanoma advances in recent years, Glaxo has a solid chance to build a name for itself in this market.

Joint disorders

Bone and joint health are common disorders that should have popped into my head earlier as a possible reason for a doctor's visit, but they are also often overlooked by investors despite accounting for 33.6% of all doctor's visits based on this study. Rather than looking to pre-existing treatments I would like to turn your attention to an up-and-coming experimental drug that has a strong chance to be a blockbuster from Merck (NYSE:MRK) known as odanacatib.

If there were any doubts about the effectiveness of odanacatib, a drug designed to reduce fracturing in bones, they flew the coop in late-stage trials when an outside monitoring committee stopped the trial early because of its overwhelming success. Although Merck is taking its time with its potential blockbuster and waiting until 2014 to file for a new drug application, it has the potential to garner $3 billion or more in peak sales if approved.

Back problems

Talk about another category that can have a bevy of problems ranging from something as minor as a muscle pull to some serious like pain caused by cancer. Back problems were named in nearly one-quarter (23.9%) of all doctors' visits and have the potential to be a big moneymaker for big pharmaceuticals and investors.

One clear way to play this is by sticking with an iconic over-the-counter medication known to relieve pain, Tylenol, which is still manufactured by Johnson & Johnson. Clearly J&J's revenue stream is incredibly diverse, with consumer products, medical devices, and pharmaceuticals combining to equal a really large pie, but you would be surprised how often physicians suggest to patients a regimen that involves over-the-counter anti-inflammation products like Tylenol to alleviate non-serious back pain.

Cholesterol problems

High cholesterol at the No. 4 spot (named in 22.4% of all doctor's visits by respondents) might be the first truly expected ailment that appeared on this list. As I mentioned earlier, with more than a third of this nation's adults being obese, this group of people runs a considerably higher risk of developing obesity-related complications, which can range from high blood pressure and high cholesterol, to more immediately serious diseases like cancer. Cholesterol-lowering drugs have the potential to make a meaningful and long-lasting impact on improving the quality of life for a good chunk of Americans, which is why pharmaceutical companies are investing so heavily in new medications now.

A new medication I've hailed as a game-changer on numerous occasions since its approval in May is Liptruzet. This combination drug, which is made up of a statin -- Pfizer's now generic Lipitor -- and Merck's cholesterol absorption inhibitor Zetia, delivered a far bigger effect on reducing LDL-cholesterol (the bad kind) than either Lipitor or Zetia could on their own in trials. Liptruzet's LDL-reduction totaled 53% to 61% as compared with Lipitor and Zetia, which demonstrated LDL-reductions of 37% to 54% and 20%, respectively. As long-term safety concerns for these revolutionary new LDL-reducing drugs lessen, the number of prescriptions written for them by physicians is likely to improve.

Upper respiratory conditions

The fifth most common reason for visiting the doctor, upper respiratory conditions, was my blind guess as the most common reason people went to the doctor before reading the Mayo Clinic's study. This broad topic, which encompassed 22.1% of respondents, can range from something as simple as a bacterial or viral infection that had settled in a patient's chest to something much more severe like cancer.

With the good likelihood that a vast majority of upper respiratory-related doctor visits have to do with some form of bacterial or viral infection, my suggestion here would be to look into flu vaccine manufacturers. Sanofi (NASDAQ:SNY), for example, developed roughly 60 million doses of its Fluzone for this past year's flu season and, by January, had sold out of many variations of the vaccine. It's a bit difficult to tell how in-demand the flu vaccine will be from one season to the next, but I believe Sanofi's sales this past year speak for themselves.

What's your reason?

Sometimes getting in ahead of the next big sales trends in the pharmaceutical industry involves looking at studies like this one and understanding why people go to their doctor in the first place. With a better understanding of why other people go see their doctor, perhaps being honest with yourself and asking yourself the same question might clue you into the next great health-care investment opportunity!