Debra Vester applied for supplemental social security income under Title XVI of the Social Security Act on September 14, 1992, claiming that she was unable to work due to her physical and mental impairments. After an initial denial, a hearing *888was held in 1993, and an adverse decision issued in 1995. In 1996, the Appeals Council of the Social Security Administration denied her request for review, but when Vester sought judicial review, the district court remanded the case for further consideration. In 199Y, a second administrative hearing was held, and an Administrative Law Judge (“ALJ”) once again denied her claim. In 1999, a second district court decision remanded her claim for further consideration. A third hearing was held on June 27, 2001, and a third ALJ decision denying her application was issued on October 25, 2001. On February 6, 2002, the Appeals Council declined to review the ALJ’s decision, and on March 17, 2004, the district court1 affirmed the Commissioner’s denial of benefits. Vester now appeals, and we affirm.
I.
An ALJ pursues a familiar five-step inquiry in determining whether a claimant is disabled. See 20 C.F.R. § 416.920. In order to qualify for benefits, the claimant must demonstrate that she suffers from a severe impairment, lasting for at least twelve continuous months, and that the impairment prevents her from performing substantial gainful work. If such an impairment exists, the ALJ must determine whether the claimant has demonstrated that she is unable to perform either her past relevant work, or any other work that exists in significant numbers in the national economy. 20 C.F.R. § 416.945.
In the most recent decision denying Vester’s application for benefits, the ALJ followed this five-step process and determined that Vester did suffer from a combination of impairments that was “severe” for purposes of the Social Security Act. Although he found that Vester’s claims regarding her limitations were not totally credible, the ALJ concluded that when all of her impairments were considered, her non-exertional limitations significantly compromised her range of work.
However, in Vester’s case, the ALJ’s duty was complicated by her long history of drug and alcohol abuse. Under 1996 amendments to the Social Security Act, if alcohol or drug abuse is a “contributing factor material to the Commissioner’s determination” of a disability, the claimant is not entitled to benefits. 42 U.S.C. § 423(d)(2)(C). In the determination whether the substance abuse is “material,” the claimant has the burden of demonstrating that she would still be disabled if she were to stop using drugs or alcohol. 20 C.F.R. § 416.935(b)(1); Pettit v. Apfel, 218 F.3d 901, 903 (8th Cir.2000).
In considering Vester’s claimed disability, the ALJ determined that, absent alcohol abuse, she had the ability to perform light work, except that she was unable to stand or walk for more than four hours out of an eight-hour work period or more than one hour without interruption, or to sit for more than six hours out of an eight-hour period or two hours without interruption. The ALJ also found that, outside of her problems with alcohol, she had a limited but satisfactory ability to deal with the public, use judgment, maintain attention and concentration, relate predictably, behave in an emotionally stable manner, and understand, remember, and carry out detailed job instructions, but a poor ability to understand, remember, and carry out complex job instructions. Based on these findings, the ALJ concluded that Vester was not disabled within the meaning of the Social Security Act.
II.
On appeal, Vester does not take issue with the ALJ’s findings with respect *889to her physical ailments, but argues only that the ALJ erred in determining that alcohol was a contributing factor material to her disability. We review the district court’s decision to uphold the denial of social security benefits de novo, and consider, as the district court did, whether the ALJ’s decision is supported by substantial evidence on the record as a whole. Harris v. Barnhart, 356 F.3d 926, 928 (8th Cir.2004). “Substantial evidence” is such evidence that a reasonable person would find adequate to support the ALJ’s determination. Sultan v. Barnhart, 368 F.3d 857, 862 (8th Cir.2004). In evaluating whether the AL J’s decision meets this standard, we consider all of the evidence that was before the ALJ, but we do not re-weigh the evidence, and we defer to the ALJ’s determinations regarding the credibility of witnesses so long as such determinations are supported by good reasons and substantial evidence. Guilliams v. Barnhart, 393 F.3d 798, 801 (8th Cir.2005).
Vester argues that her- alcoholism is not a contributing factor material to her claimed disability. As Vester pointed out to the ALJ and in her argument before this court, there is evidence to support her assertion that she has suffered, at times, from mental illness. As early as 1991, she began seeing Penny Wenczel, a Licensed Certified Social Worker, for therapy to treat recurrent moderate depression. (R. at 173). In 1993, B. Eliot Cole, M.D., diagnosed Vester with bipolar disorder and major depression, along with a probable personality disorder, placing her “Global Assessment of Functioning” level at 55 to 60 on a scale of 0 to 100. (R. 181.) The Commissioner’s doctor, Gene W. Reid, M.D., examined Vester on February 19, 1997, and diagnosed her with bipolar disorder (although in remission), alcohol dependence, and personality disorder. (R. 480.) In 1998, Terry Sutterfield, M.D., treated Vester and echoed the diagnoses of depression and probable personality disorder. (R. 712.) In addition, at several points between 1992 and 1995, Vester sought therapy from Joan Shepard, a Licensed Professional Counselor.
At the same time, much of Vester’s medical history suggests that alcohol has been a substantial barrier to her normal functioning. After showing up intoxicated for an appointment in 1991, she went through a period of sobriety during which she was doing “quite well” and had no need for medication. (R. at 171, 165). The sobriety was short-lived, however; notes from her therapy with Joan Shepard are replete with references to-Vester’s use of alcohol. (R. at 229, 233, 298). The same doctors who diagnosed her with depression also noted her alcohol dependence (R. at 181, 481, 712), and at her. 2001 hearing, Vester testified that she had only been sober “periodically.” (R. at 584). While Vester testified that her last ten years included a streak of sobriety as long as three years (R. at 584), she also sustained two convictions for driving while intoxicated during that period. (R. at 409-10).2
*890In urging that we reverse the Commissioner’s findings, Vester points to elements of the record that she says support her claim that she is disabled independent of her alcoholism. A1998 letter from Joan Shepard, the counselor who treated Vester, asserted that “alcoholism has been Mrs. Vester’s way of self medicating her underlying problems” and that her need for benefits “is based on the mental health issues.” (R. at 687). The ALJ did not credit this letter. Noting that Shepard has no medical degree and did not qualify as a medical source under the regulations, he nonetheless considered the opinion and Shepard’s clinical notes, but found the notes to be unsupportive of the letter’s content. As the ALJ noted, Shepard had seen Vester only sporadically and never for more than a year continuously. Moreover, notes from another therapist at Shepard’s clinic indicated that Vester “need[ed] to be in treatment for alcohol dependence] before any other treatment,” (R. at 207), a conclusion that is consistent with the ALJ’s determination that Vester’s alcoholism was a material factor contributing to her disability.
Vester counters that Shepard’s 1998 letter was co-signed by a psychiatrist, C.G. Pearce, M.D., and should therefore be credited as a medical opinion. Other than Dr. Pearce’s signature on the letter, however, Vester points to no medical records or other evidence indicating his involvement in Vester’s treatment, and we find no reason to require that the ALJ credit the letter as the opinion of a “treating” psychiatrist. In addition, some of the ALJ’s reasons for discrediting Shepard — especially the irregularity of her visits with Vester — also extend to Dr. Pearce, who was employed by the same clinic as Shepard and would not have seen Vester any more frequently than Shepard. We believe that the ALJ properly considered the letter and gave good and adequate reasons for his decision not to give the opinion substantial weight.
Vester’s general attacks on the ALJ’s findings that she was functioning normally while sober also fail. While it is true that “[determining whether a claimant would still be disabled if he or she stopped drinking is, of course, simpler if the claimant actually has stopped,” Pettit, 218 F.3d at 903, in this case Vester had been sober only five months at the time of her 2001 hearing before the ALJ, and she admitted that her sobriety was “periodic[ ].” (R. 584.) Nonetheless, there is some evidence in the record of her improved condition during other periods of sobriety. At many such times, notes from Shepard and others indicate that Vester is “doing well” (R. at 221) and “feeling good” (R. at 209). During one period of sobriety, Vester was able to attend classes and complete a 90-day community service assignment.3 In Shepard’s notes regarding that assignment, she remarked on the “respect that [Vester] has gained” at Marshall Nursing Home, and wrote that Vester had been volunteering five days and attending classes two days each week. (R. at 503-04). In fact, Ves-ter’s performance in the community service program was so promising that her *891supervisor sponsored her for a Certified Nurse Assistant class, which Vester. completed. (R. 503, 508, 510).
Notwithstanding the above-described evidence upon which the ALJ rested his finding that Vester would be not disabled absent her alcoholism, Vester argues that there must be additional “medical evidence” to support the ALJ’s findings with respect to Vester’s residual functional capacity. See Lauer v. Apfel, 245 F.3d 700, 704 (8th Cir.2001). She contends that the opinion of Dr. Reid, the psychiatrist, is insufficient to support the ALJ’s conclusion, because the doctor merely included Vester’s alcoholism in his evaluation “without considering what limitations would remain in the absence of the alcoholism.” (Appellant’s Reply Br. at 6).
We have some doubt whether Vester’s ability to work in the absence of alcoholism is a “medical question” comparable to the traditional determination of residual functional capacity. Put simply, if an ALJ is presented with evidence that a claimant has demonstrated the ability to work during periods of sobriety, it seems within the ken of the ALJ to make a factual finding that the claimant is able to work when' she is not abusing alcohol. This sort of judgment, based largely on historical facts, strikes us as different in kind from that required when a claimant presents a set of medical problems, and the ALJ must make a predictive judgment as to the claimant’s ability to work in light of a given medical condition.
Assuming for the sake of argument, however, that the ALJ was required to develop some medical evidence, we believe the record is adequate to support the ALJ’s decision. Although Dr. Reid did not phrase an opinion precisely in terms of the statutory framework of the 1996 amendments to the Social Security Act, we believe that his evaluation does include “some supporting evidence from a professional,” Lauer, 245 F.3d at 704, that bolsters the ALJ’s conclusion. When asked to “describe any limitations” and to “include the medical/clinical findings” that supported his assessments that Vester was limited in certain functions, Dr. Reid observed that she was a “severe alcoholic,” that she has “some difficulty with thought organization — probably from years of alcohol abuse,” that she suffered from “long term alcoholism with very little sobriety,” and that her alcoholism dependence was only “In Partial Remission.” (R. at 480-82). He opined that her condition “[m]ay improve with more time sober and taking mood stabilizing medication.” (R. at 480). While Dr. Reid noted elsewhere that Ves-ter “also has Bipolar Disorder,” (R. at 482), he concluded that this condition was “In Remission.” (R. at 480).
We agree with the district court that “[ajlthough Dr. Reid also diagnosed bipolar disorder, it is clear that he believed [Vester’s] main problem leading to her functional limitation was her long-term alcoholism.” (Mem. and Order, Mar. 17, 2004, at 4). We believe, therefore, that it was reasonable for the ALJ to conclude that Dr. Reid’s evaluation provided some medical evidence in support of a conclusion that Vester’s alcoholism was a material factor contributing to her disability, and that the record was adequately developed on this point.
. After considering all of the evidence under the substantial evidence standard, we are satisfied, that the ALJ case untangled Ms. Vester’s history of alcoholism and mental illness with sufficient clarity and detail to support the finding that she is not disabled apart from her alcoholism. In contrast to other cases involving alcohol abuse that have been remanded to the ALJ for reconsideration, e.g., Brueggemann v. Barnhart, 348 F.3d 689, 695-96 (8th Cir.2003); Pettit, 218 F.3d at 903-04, the *892ALJ followed the analytical framework prescribed by the regulations, made detailed factual findings about Vester’s depression and alcoholism, and supported his findings with references to the record. We conclude that a reasonable person considering the record as a whole could reach the conclusion adopted by the ALJ.
íJí jfc ifc $
For the reasons detailed above, we conclude that substantial evidence supports the Commissioner’s finding that Vester is not disabled under the Social Security Act when she is not abusing drugs or alcohol. We therefore affirm the judgment of the district court.
. The Honorable Henry L. Jones, Jr., United States Magistrate Judge for the Eastern District of Arkansas, presiding by consent of the parties.
. At the administrative hearing, the ALJ asked the medical expert, Dr. Patricia Griffen, whether, if Vester “stuck with strict sobriety and took the medications as she is directed, would you expect her condition to substantially improve?” She answered:
I don't know if I can answer that in terms of whether or not it would substantially improve. However, in cases where individuals have been able to remain sobriety, abstinent from alcohol, follows through in treatment for the depression, there certainly has been a history of improvement with those individuals. And to what extent that would be substantial, I don't know. But certainly the alcohol worsens the depression and interferes with the individual level of functioning.
(R. 600).
. Vester argues that this history supports her claim that she is unable to function continuously even while sober, because the assignment took her "five months” to complete, rather than the assigned 90 days, and because she was "written up” for being argumentative. However, the only evidence that Vester points to in support of these problems is her own testimony. (R. at 399-400). Her assertion that it took her five months to complete the assignment is in conflict with other evidence in the record, including Shepard’s notes indicating that Vester was sentenced to community service on January 17, 1997, and that she had definitely completed the service by the time of her meeting with a judge on May 1, 1997. (R. at 496, 510).