If you’ve been given an HPV diagnosis or have been told that you have ‘precancerous’ cervical changes or cervical dysplasia, there’s a good chance you’re freaking out. It’s a scary thing to hear, and often, the information isn’t delivered with the whole picture: namely that most HPV infections clear up on their own and most pre-cancerous lesions resolve spontaneously, with very little risk that they will progress to cancer.
That said, cervical cancer does affect about 12,000 women in the US each year, and take the lives of just over 4,000. While most cases of cervical cancer are in older women who have not had proper pap or HPV testing, each year hundreds of thousands of women will receive the ‘diagnosis’ that they have a bad pap.
In recent episodes of Natural MD Radio (and the corresponding blogs), I gave you all the details you need to understand what HPV is, and how to make sense of test results.
While appropriate conventional follow-up testing and treatment are absolutely essential with HPV and all cervical changes, and are part of a safe, healthy integrative approach, I'd like to share what's known about the natural approaches that have been researched with some promising results that women might want to use, not as a substitute, but while waiting to do follow-up testing for mild to moderate cervical changes. Listen to the Natural MD episode by clicking on the player above, or read the blog below.
HPV or a “Bad Pap”: Can You Wait and Watch?
In most cases of mild to moderate cervical changes, we’re told to wait and repeat testing in a year; sometimes additional follow-up testing is done immediately – but even when that is necessary, the verdict remains the same: wait and retest in a year. This is a medically legitimate approach and if you're comfortable with that, you can stop reading here, no harm, no foul.
- But is there more you can do in that interim instead of carrying that small (or large) annoying anxiety in the back of your mind until that retest date rolls around in next year’s calendar?
- What if you have chronic HPV and want to do something about it now?
- And are there any root causes associated with HPV or cervical changes that you can be proactive about addressing, to increase the likelihood that you’ll only have positive tests going forward?
That’s exactly what Katie wanted to know when she came to see me.
At 32, her doctor told her she had mild cervical dysplasia; further testing showed she was positive for HPV. She told her to wait and watch, and if her follow-up testing was positive, she’d need a colposcopy and possible cervical biopsy. But Katie had already been struggling to get pregnant for two years now, and the idea of doing something that could lead to scarring on her cervix and further interfere with fertility added to her anxiety. A friend told her to come see me, and she did.
A Holistic Approach to Cervical Health
Because mild cervical dysplasia and HPV both have such a high rate of spontaneous regression, meaning they clear on their own, simply waiting, without feeling like you have to do anything special, is certainly an option. But like Katie, most women who come to see me, or who write to me with concerns about these issues, want to do something. Further, there is the risk, albeit low, that in a year’s time, those cervical changes or HPV won’t have reverted to normal, or, worse, they will have become chronic or progressed.
In my personal opinion as a medical doctor and midwife specializing in women’s health and natural medicine, why not take the initiative and be preemptive with safe approaches? It’s still absolutely important to follow-up with appropriate cervical screening per the recommended guidelines, but being hands-on and preemptive can help you to address some of the possible underlying causes of chronic HPV, cervical changes, and known susceptibilities to cervical cancer, which only improve overall wellness.
There are four root areas to consider when it comes to addressing factors that can possibly contribute to cervical changes, persistent HPV infection, and even cervical cancer. Addressing these can be a supportive route to restoring optimal cervical health preventing chronic HPV infection, and reduce risk of progression to cervical cancer.
The 4 Roots are:
- The Nutrient Connection
- Inflammation and Oxidative Damage
- Stress and Immunity
- The Vaginal Microbiome
Let’s take a look at these together.
The Nutrient Connection
Most women are significantly low in many important nutrients – including those especially important for optimal immunity cervical health. Studies have found a number of these to be low in women in women with cervical cancer including folate, Vitamin A, selenium, vitamin D and B12. Therefore, making sure you’re getting enough of these in your diet by getting ideally 8 to 10 servings of brightly colored fruits and veggies, with an emphasis on organic leafy greens and berries (important because of the high number of pesticides in these), and through appropriate supplementation may make a difference in preventing cervical changes and HPV from progressing.
If you already have cervical changes or positive HPV, increasing dietary intake may not be enough – in this case, if a supplement is suggested, consider adding that to your daily plan in addition to improving dietary intake.
Folate
Folate is a B-vitamin that is naturally present in many foods. Your body needs folate to make DNA and other genetic material. Your body also needs folate for your cells to divide. A form of folate, called folic acid, is used in fortified foods and most dietary supplements. As such, it appears to play an important role in cervical health.
For example, a group of 58 women with cervical dysplasia seen on colposcopy (CIN1), ages 18 to 58, were enrolled in a randomized, double-blind, placebo controlled study, and divided into two groups. For 6 months, half received 5 mg/day folate supplements, half received placebo. A greater percentage of women in the folate group (83.3%) had regressed CIN1 vs. 52 % in the placebo group, and blood levels confirmed the association with higher folate levels. Higher folate has, in other studies, been associated with significantly lower risk of CIN, especially when vitamin B12 levels are also sufficient. Vegans are commonly low in B12. A simple blood test for either B12, or an even more accurate test called MMA, can give you insight into your level and can be done by any licensed medical professional.
An association between the MTHFR C677T snp, which interferes with the ability to use folate and folic acid from the diet, has been found to play an important role in many cancers, likely due to its roles in detoxification and cellular repair. While a meta-analysis of 12 studies looking at the relationship between MTHFR SNPs and cervical cancer did not demonstrate a connection specifically, the researchers did not discount the possible importance of this relationship. In my practice, I use a methylfolate supplement for women with cervical dysplasia at a 5 mg/day dose, and put most women with the MTHFR snp on 800 mcg of methylfolate regardless of cervical changes, as part of a general daily multivitamin or safe stand-alone supplement. The higher dose is only recommended as part of a cervical dysplasia treatment plan.
- To get more folate in your diet: increase your intake of leafy green vegetables, and also beans.
- To get more B12 in your diet: include fish, meat, poultry, eggs, dairy products, or nutritional yeast; if you’re a vegan, a supplement is essential.
- To supplement:
- Methylfolate, 5 mg/day
- Vitamin B12 1000 mcg sublingual, daily
Beta-Carotene
Vitamin A appears to have an important impact on cervical health and development of cervical cancer. In one major scientific review evaluating 11 articles on dietary Vitamin A and four articles on blood levels of Vitamin A for a total of 12,136 participants, higher dietary Vitamin A intake and blood levels of Vitamin A were inversely associated with the risk of cervical cancer. In one study of 191 women with cervical cancer and 191 women of the same age who did not have cervical cancer, there was no association between dietary Vitamin A and cervical cancer risk, however, dietary intake of beta-carotene, on the other hand, was strongly related to a lower risk of cervical cancer. In fact, women with higher beta-carotene intake seem to have about less than half of the risk. In yet another study, increased beta-carotene in the diet reduced the risks of pre-invasive cancer (the kind that shows up as mildly abnormal cervical cells on Pap smears) but not on invasive cervical cancer (much more rare).
- To get more beta-carotene in your diet: The top food sources include carrots, broccoli, cantaloupe, and squash. Overall, aim for 6-8 servings of leafy green vegetables, orange and yellow vegetables, and tomatoes in your daily diet.
- To supplement: A portion of the Vitamin A in some supplements is in the form of beta-carotene and the remainder is preformed Vitamin A; look for supplements that provide beta-carotene at about 3000 mcg/day
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Inflammation and Oxidative Stress
Inflammation is your body's way of protecting itself from infection, illness, or injury. As part of the inflammatory response, your body increases its production of white blood cells, immune cells, and substances called cytokines that help fight infection. However, when inflammation gets out of control, it’s a bit like a fire that gets out of your fireplace and into your home!
Numerous factors increase inflammation, most notably, a diet high in refined carbs and sugar, and ultra-processed foods, too much meat and too little fruits and veggies, low nutrient intake, exposure to environmental toxins – which we all get daily – as well as chronic stress and lack of good sleep, just to start the list! Oxidative stress is also a natural process, but like inflammation, when it’s out of control, meaning in this case, when there’s an imbalance of free radicals compared to antioxidants in the body, cell and tissue damage can occur. Further, oxidative stress leads to inflammation, and vice versa, in a vicious cycle.
How does this relate to cervical health? Well, our bodies are one interconnected organism, and inflammation and oxidative stress can alter cervical cell health and make them more vulnerable. In fact, studies have also shown that increased inflammation and oxidative stress may result in higher concentrations of HPV in the cervical and vaginal secretions which then make the cervical cells more vulnerable to cellular damage.
It’s super important to take an overall approach to reducing inflammation and oxidative stress. Here are the biggies that can help:
- Eliminate all ultraprocessed foods, refined sugar, and carbs from your diet. Seriously, they can cause major inflammation. An elimination diet is a great way to get started, and can also help you identify personal food triggers.
- Get 8 to 10 servings of fresh veggies and fruits in your diet EVERY DAY. Here’s a green drink to help you on your way. This plus 1 cup of berries daily and you’re more than halfway there. Add a salad and a sweet potato and you’re golden – plus you’ve gotten a healthy supply of folate and Vitamin A!
Gingery Lemon Green Juice
In a Vita Mix, blend:
- 2 cups of spinach, chard, parsley
- ½ cup frozen berries (unless you absolutely can’t tolerate fruit)
- Juice of ½ lemon
- 1 thin slice of fresh ginger root (optionally, if you have access, you can also add several thin slices of fresh turmeric root or ½ tsp. turmeric powder)
- 1 cup of water (or almond milk or coconut water) and crushed ice
Also, work on stress and get more sleep. Thinking yes, but how the heck to? Here is a blog to get you started, and my book, The Adrenal Thyroid Revolution has your name all over it! If you take it regularly, find reliable alternatives to Tylenol which rapidly eats up that detoxifying glutathione.
The following supplements may specifically play a role in oxidative stress and cervical health.
Selenium
Medical studies have provided evidence of selenium supplementation in preventing certain cancers. Low and too high selenium (Se) status are associated with increased risk of lung, larynx, colorectal and prostate cancers. A higher level of selenium and supplementation with selenium has been shown to be associated with substantially reduced cancer mortality. Selenium is an important mineral in protecting the body from oxidative stress (discussed below) – the harmful impact of heavy metals and other harmful substances – on our health.
While not all studies have shown a relationship between serum selenium and cervical cancer, some have shown an inverse relationship between serum selenium levels and CIN, as well significantly lower concentration of selenium in cervical cancer tissues compared to non-cervical cancer tissues, and a protective effect in former smokers. In one study, 58 women with biopsy-proven CIN 1 were randomized to take 200 mcg selenium per day or placebo for 6 months. The selenium group had regression of their CIN1 compared with the placebo group.
Selenium rich foods include, by micrograms per serving:
Brazil nuts, 1 ounce (6–8 nuts) | 544 |
Tuna, yellowfin, cooked, dry heat, 3 ounces | 92 |
Halibut, cooked, dry heat, 3 ounces | 47 |
Sardines, canned (oil), drain solids w/bone, 3 oz. | 45 |
Shrimp, canned, 3 ounces | 40 |
Beef steak, bottom round, roasted, 3 ounces | 33 |
Turkey, boneless, roasted, 3 ounces | 31 |
Chicken, light meat, roasted, 3 ounces | 22 |
Cottage cheese, 1% milkfat, 1 cup | 20 |
Rice, brown, long-grain, cooked, 1 cup | 20 |
Source: https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/#h3
- To supplement take 200 mcg/day (do not exceed this daily dose)
Glutathione (GSH)
Glutathione is a naturally occurring combination of three amino acids (cysteine, glutamic acid, and glycine) present in most human tissue. It acts as an antioxidant, a free radical scavenger and a detoxifying agent in cells, and is important in liver detoxification of hormones, many medications (including Tylenol), and environmental toxins.
GSH also helps to repair cellular damage from oxidative stress. When the body is under cellular stress from high levels of exposure to any of these, our demand for GSH goes up as we more quickly burn through what our body naturally produces each day. Studies have demonstrated low GSH levels in women with cervical cellular changes. Additionally, plasma glutathione (GSH) levels were significantly increased in the folate group compared to the placebo.
Glutathione can be taken directly as a supplement, but it doesn’t absorb well. Instead, it’s best to use supplements that your body can use to make GSH. The best is NAC, a supplement form of the naturally occurring amino acid cysteine. Vitamin C also raises red blood cell glutathione by nearly 50% after just 500 mg /day. Additionally, methylfolate, selenium and curcumin have all been shown to increase GSH levels.
- To supplement: NAC: 300 to 900 mg, 3x/day
Green Tea
Research suggests that green tea extract and EGCG, a, antioxidant component of green tea, can inhibit the proteins and genetic changes that HPV causes in cervical cells that can lead to cervical cancer. These constituents in green tea, called catechins, are also antiviral, antiproliferative and immunostimulatory. Several studies have shown that topically, green tea extracts can clear genital warts due to HPV, and in fact, it’s so effective that pharmaceutical development of these products is being explored. There is less data on the impact of the strains of HPV that cause cervical cell changes, but the data is so strong for the other stains of HPV causing warts, that I personally feel it is worthwhile to include a green tea supplement as part of a protocol, at least for persistent HPV, that in my practice I do. Drinking a reasonable amount of green tea every day wouldn’t give you enough of what you need, so supplementing is the way to go.
- To supplement: Use a product standardized to 500 mg ECGC daily, not to exceed this dose
Curcumin
Curcumin has been shown, in oral doses, to have anticancer activity and cause regression of premalignant lesions in several tissues including the cervix. Several studies have demonstrated that curcumin treatment alters HPV-associated molecular pathways in cancer cells and suppresses cervical cancer growth. In one study, 287 women with HPV were randomized into four groups to be treated with vaginal Basant cream (containing curcumin extract), vaginal placebo cream, curcumin vaginal capsules or placebo vaginal capsules respectively. After 30 days of consecutive application, the women with Basant cream treatment demonstrated the highest HPV clearance rate (87.7%) compared to the control groups (73.3%.) In my practice I use curcumin also because it helps to increase glutathione and support detoxification.
- To supplement: Curcumin is included in products, or available alone, in usually one of two ways:
- Meriva®, a patented combination of curcumin and soy lecithin, take 500 mg twice a day;
- Curcumin with piperine (from black pepper), take 500 mg of the former with 20 mg of the latter, three times/day
DIM and Indole-3-Carbinol (I3C)
Current research suggests that DIM, a broccoli extract taken as a supplement, may function as a chemopreventive agent. A mouse study demonstrated that DIM inhibited the formation of HPV cervical lesions. A recent pilot study tested DIM to treat CIN2 or 3 changes. Sixty-four women scheduled for LEEP were administered a 12-week course of DIM (at a dose of 2 mg/kg daily) or placebo, with evaluations occurring every 3-4 months for one year. The measurements included pap smear, HPV, colposcopy, biopsy and physical examination. At the 6-month follow up, 85% of subjects did not require LEEP based on improving global assessment. However, no statistically significant differences were observed between the DIM and placebo group. What these results really tell us is that in 6 months, many women will have spontaneous improvement in cervical health regardless of whether there is treatment. Another study observed apoptotic effects of indole-3-carbinol (another broccoli extract supplement), meaning that it induced the death of cervical cancer cells in vitro (not in an animal or person).
Both DIM and I3C are popular components in many naturopathic cervical health protocols. Though their effectiveness is still to be determined, they are safe and reasonable to include. However, if you’re being mindful of your supplement budget, which can add up quickly, you might just skip this one in favor of the most promising natural therapies (listed below).
- To supplement: Typical dose (can be combined, or use one or the other):
- DIM: 100mg/day
- `I3C: 200 mg/day
The Vaginal Microbiome and Cervical Health
Bacteria are increasingly appreciated as a key player in the initiation and progression of other malignancies including colorectal cancer. Evidence suggests that the vaginal microbiome plays a functional role in the persistence or regression of HPV infections. Vaginal microbial diversity and richness appear to be not only associated with HPV infection, but also with advancing CIN severity. Increasing disease severity was also found in one study to be associated with decreasing relative abundance of Lactobacillus spp.
Beneficial vaginal microorganisms, which form part of the vaginal microbiome, especially Lactobacillus spp. are thought to defend against pathogens and sexually transmitted infections through maintenance of a pH that is hostile to them, production of species-specific metabolites, bacteriocins and through adherence to mucous and disruption of biofilms. BV (also associated with Lactobacillus spp.) depletion and increased diversity of potentially pathogenic gram negative bacteria, is associated with significantly higher rates of HPV infection and CIN.
HPV infection itself may adversely impact your normal, healthy cervical cell immune defenses leading to aberration of vaginal microbiota, promoting HPV persistence and disease progression. Diet, stress, and many other environmental and hormonal factors are also known to modulate the vaginal microbiome.
To Restore Vaginal a Healthy, Diverse Vaginal Microbiome
You can learn much more about restoring a healthy vaginal microbiome here, an important part of this plan to restore cervical health.
I do recommend a daily probiotic combination, which can be used just orally, or both orally and vaginally (simply insert as a suppository each night before bed) to include strains of Lactobacilli that have been shown to be specifically beneficial for supporting healthy vaginal flora.
- L.rhamnosus
- L. reuteri
- L. crispatus
Stress, Immunity, and Cervical Health
Stress has an enormous impact on immune function, so stress reduction and self-care are important parts of any plan to reduce inflammation and improve immunity. Adaptogens can also be considered, along with lifestyle approaches to stress reduction. One of my favorite adaptogens for immune health is Ciriolus versicolor (Turkey tail) extract 3000 mg/day, which is really added more for immune system support than stress reduction, so I combine it with ashwagandha, Rhodiola, holy basil, or others. You can learn all about adaptogens for improving your stress response here.
Additionally, I often include St. John's Wort and Lemon Balm in my protocols for HPV, usually in tincture form. While studies don't show a direct correlation between these herbs and HPV, they are historically used by herbalists like myself for their antiviral activity (they do have known action against HSV, or the herpes virus) and because they are supportive for the nervous system. Numerous studies support the use of St. John's Wort for anxiety and depression.
Cervical Health Supplement List At-a-Glance
Bringing it all together, here’s a list of the supplements I use in my practice:
- Folic Acid: in the form of methylfolate, 5 mg/day (+ B12 if low levels)
- Beta-carotene up to 3000 mcg/day
- NAC 300 to 900 mg, 3 times daily
- Curcumin, see dosages above in article
- Selenium, 200 mcg/day
- Green Tea Extract standardized to EGCGs, 500 mg/day
- Turkey Tail extract, 3000 mg/day
- Daily probiotic containing L. rhamnosus, L. reuteri, L. crispatus
- Consider St. John's Wort 300 mg 3x/day
I ask my patients to follow this protocol for 3-12 months, while continuing with the recommended Pap smears and appropriate evaluations. Most are thrilled with the results! For example, in 6 months, Katie was HPV-free with a normal pap smear, and has remained that way for several years now. And, I can delightedly share, she conceived a baby within just a few months of the ‘all clear’ and had a beautiful pregnancy and birth.
Wellness Trends to Avoid
These popular therapies have questionable safety at best; I recommend avoiding them:
- Escharotic treatments, which can do serious damage to the cervix, even when used under the care of an experienced naturopath or MD
- Thuja, which can be toxic if systemically absorbed at a high enough dose.
Are You a Women’s Health Practitioner Who Wants to Learn More About Natural Medicine?
- If you love this information and want more like it, whether for yourself, the women in your life, or your health practice, you might really love my course Herbal Medicine for Women, which is on sale now (thru July 5, 2019) and has ongoing admission. Learn more about this course here:
- If you’re a certified or licensed health professional looking for solid training and immediately applicable tools to help make your clients’/patients’ lives better, without having to figure it all out on your own, my 10-month training, The Women’s Functional and Integrative Professional Training Program might just be calling your name. Registration is only open for a limited time. Learn more about this one here.
References
Ahmad, N., Cheng, P., & Mukhtar, H. (2000). Cell Cycle Dysregulation by Green Tea Polyphenol Epigallocatechin-3-Gallate. Biochemical and Biophysical Research Communications,275(2), 328-334.
Aroutcheva, A., Gariti, D., et al. Faro, S. (2001). Defense factors of vaginal lactobacilli. American Journal of Obstetrics and Gynecology,185(2), 375-379.
Asemi, Z., Vahedpoor, Z., et al. (2016). Effects of long-term folate supplementation on metabolic status and regression of cervical intraepithelial neoplasia: A randomized, double-blind, placebo-controlled trial. Nutrition,32(6), 681-686.
Basu, P., Dutta, S., et al. (2013). Clearance of Cervical Human Papillomavirus Infection by Topical Application of Curcumin and Curcumin Containing Polyherbal Cream: A Phase II Randomized Controlled Study. Asian Pacific Journal of Cancer Prevention,14(10), 5753-5759.
Boskey, E., Cone, R., et al. (2001). Origins of vaginal acidity: High d/l lactate ratio is consistent with bacteria being the primary source. Human Reproduction,16(9), 1809-1813.
Botezatu, A., Socolov, D., et al. (2013). Methylenetetrahydrofolate reductase (MTHFR) polymorphisms and promoter methylation in cervical oncogenic lesions and cancer. Journal of Cellular and Molecular Medicine,17(4), 543-549.
Chen, D., Qi, M., et al. (2001). Indole-3-Carbinol and Diindolylmethane Induce Apoptosis of Human Cervical Cancer Cells and in Murine HPV16-Transgenic Preneoplastic Cervical Epithelium. The Journal of Nutrition,131(12), 3294-3302.
Gattoc, L., Frew, P. M., et al. (2016). Phase I dose-escalation trial of intravaginal curcumin in women for cervical dysplasia. Open Access Journal of Clinical Trials,Volume 9, 1-10.
Gupta, S., Jaworska-Bieniek, K., et al. (2013). Can selenium be a modifier of cancer risk in CHEK2 mutation carriers? Mutagenesis,28(6), 625-629.
He, L., Zhang, E., et al. (2013). (−)-Epigallocatechin-3-gallate inhibits human papillomavirus (HPV)-16 oncoprotein-induced angiogenesis in non-small cell lung cancer cells by targeting HIF-1α. Cancer Chemotherapy and Pharmacology,71(3), 713-725.
Karamali, M., Nourgostar, S., et al. (2015). The favourable effects of long-term selenium supplementation on regression of cervical tissues and metabolic profiles of patients with cervical intraepithelial neoplasia: A randomised, double-blind, placebo-controlled trial. British Journal of Nutrition,114(12), 2039-2045.
Kim, S. Y., Kim, J. W., et al. (2003). Changes in Lipid Peroxidation and Antioxidant Trace Elements in Serum of Women With Cervical Intraepithelial Neoplasia and Invasive Cancer. Nutrition and Cancer,47(2), 126-130.
Martin, D. H. (2012). The Microbiota of the Vagina and Its Influence on Women’s Health and Disease. The American Journal of the Medical Sciences,343(1), 2-9.
Mcmillan, A., Dell, et al. (2011). Disruption of urogenital biofilms by lactobacilli. Colloids and Surfaces B: Biointerfaces,86(1), 58-64.
Mitra, A., Macintyre, D. A., et al. (2015). Cervical intraepithelial neoplasia disease progression is associated with increased vaginal microbiome diversity. Scientific Reports,5(1).
Montemarano, N., Priore, G. D., et al. (2007). Oral diindolylmethane (DIM): A nonsurgical treatment for cervical dysplasia. Fertility and Sterility,88.
Piyathilake, C. J., Macaluso, M., et al. (2009). Lower Risk of Cervical Intraepithelial Neoplasia in Women with High Plasma Folate and Sufficient Vitamin B12 in the Post-Folic Acid Fortification Era. Cancer Prevention Research,2(7), 658-664.
Stockfleth, E., Beti, H., et al. (2008). Topical Polyphenon®E in the treatment of external genital and perianal warts: A randomized controlled trial. British Journal of Dermatology,158(6), 1329-1338.
Tatti, S., Swinehart, J. M., et al. (2008). Sinecatechins, a Defined Green Tea Extract, in the Treatment of External Anogenital Warts. Obstetrics & Gynecology,111(6), 1371-1379.
Vecchia, C. L., Franceschi, S., et al. (1984). Dietary vitamin A and the risk of invasive cervical cancer. International Journal of Cancer,34(3), 319-322.
Vecchia, C. L., Decarli, A., et al. (1988). Dietary vitamin A and the risk of intraepithelial and invasive cervical neoplasia. Gynecologic Oncology,30(2), 187-195.
Yi, K., Yang, L., et al. (2016). The association between MTHFR polymorphisms and cervical cancer risk: A system review and meta analysis. Archives of Gynecology and Obstetrics,294(3), 579-588.
Yu, L., Chang, K., et al. (2013). Association between Methylenetetrahydrofolate Reductase C677T Polymorphism and Susceptibility to Cervical Cancer: A Meta-Analysis. PLoS ONE,8(2).